Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $184.43   9.690%   $202.3013   $202.30   $202.30   $202.30  
  Purchase #2 $236.97   11.841%   $265.0296   $265.03   $265.05   $265.00  
  Purchase #3 $180.81   7.361%   $194.1194   $194.12   $194.10   $194.10  
  Purchase #4 $98.33   12.543%   $110.6635   $110.66   $110.65   $110.70  
  Purchase #5 $125.99   5.292%   $132.6574   $132.66   $132.65   $132.70  
  Purchase #6 $116.25   3.258%   $120.0374   $120.04   $120.05   $120.00  
  Purchase #7 $153.28   11.759%   $171.3042   $171.30   $171.30   $171.30  
  7 purchase totals = $1,096.06       $1,196.1128   $1,196.11   $1,196.10   $1,196.10