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 $104.67   11.283%   $116.4799   $116.48   $116.50   $116.50  
  Purchase #2 $172.31   3.837%   $178.9215   $178.92   $178.90   $178.90  
  Purchase #3 $65.51   5.448%   $69.079   $69.08   $69.10   $69.10  
  Purchase #4 $232.53   6.212%   $246.9748   $246.97   $246.95   $247.00  
  Purchase #5 $236.89   3.575%   $245.3588   $245.36   $245.35   $245.40  
  Purchase #6 $114.44   9.107%   $124.8621   $124.86   $124.85   $124.90  
  Purchase #7 $150.82   12.818%   $170.1521   $170.15   $170.15   $170.20  
  7 purchase totals = $1,077.17       $1,151.8282   $1,151.82   $1,151.80   $1,152.00