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 $141.92   6.644%   $151.3492   $151.35   $151.35   $151.30  
  Purchase #2 $101.79   13.504%   $115.5357   $115.54   $115.55   $115.50  
  Purchase #3 $207.80   5.371%   $218.9609   $218.96   $218.95   $219.00  
  Purchase #4 $211.84   9.799%   $232.5982   $232.60   $232.60   $232.60  
  Purchase #5 $84.68   10.643%   $93.6925   $93.69   $93.70   $93.70  
  Purchase #6 $175.78   13.721%   $199.8988   $199.90   $199.90   $199.90  
  Purchase #7 $82.71   9.201%   $90.3201   $90.32   $90.30   $90.30  
  7 purchase totals = $1,006.52       $1,102.3554   $1,102.36   $1,102.35   $1,102.30