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 $88.27   7.779%   $95.1365   $95.14   $95.15   $95.10  
  Purchase #2 $226.59   8.404%   $245.6326   $245.63   $245.65   $245.60  
  Purchase #3 $146.96   9.393%   $160.764   $160.76   $160.75   $160.80  
  Purchase #4 $63.47   3.634%   $65.7765   $65.78   $65.80   $65.80  
  Purchase #5 $219.61   11.499%   $244.863   $244.86   $244.85   $244.90  
  Purchase #6 $29.86   5.284%   $31.4378   $31.44   $31.45   $31.40  
  Purchase #7 $76.76   4.210%   $79.9916   $79.99   $80.00   $80.00  
  7 purchase totals = $851.52       $923.6020   $923.60   $923.65   $923.60