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 $84.49   13.507%   $95.9021   $95.90   $95.90   $95.90  
  Purchase #2 $235.98   13.571%   $268.0048   $268.00   $268.00   $268.00  
  Purchase #3 $78.66   4.380%   $82.1053   $82.11   $82.10   $82.10  
  Purchase #4 $214.26   13.817%   $243.8643   $243.86   $243.85   $243.90  
  Purchase #5 $74.60   7.631%   $80.2927   $80.29   $80.30   $80.30  
  Purchase #6 $57.94   7.510%   $62.2913   $62.29   $62.30   $62.30  
  Purchase #7 $124.25   3.158%   $128.1738   $128.17   $128.15   $128.20  
  7 purchase totals = $870.18       $960.6343   $960.62   $960.60   $960.70