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 $119.95   11.809%   $134.1149   $134.11   $134.10   $134.10  
  Purchase #2 $107.94   8.134%   $116.7198   $116.72   $116.70   $116.70  
  Purchase #3 $226.84   3.302%   $234.3303   $234.33   $234.35   $234.30  
  Purchase #4 $163.55   9.174%   $178.5541   $178.55   $178.55   $178.60  
  Purchase #5 $196.86   6.831%   $210.3075   $210.31   $210.30   $210.30  
  Purchase #6 $93.54   3.547%   $96.8579   $96.86   $96.85   $96.90  
  Purchase #7 $98.41   10.444%   $108.6879   $108.69   $108.70   $108.70  
  7 purchase totals = $1,007.09       $1,079.5724   $1,079.57   $1,079.55   $1,079.60