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 $57.84   13.139%   $65.4396   $65.44   $65.45   $65.40  
  Purchase #2 $128.87   4.718%   $134.9501   $134.95   $134.95   $135.00  
  Purchase #3 $103.59   13.675%   $117.7559   $117.76   $117.75   $117.80  
  Purchase #4 $238.30   10.441%   $263.1809   $263.18   $263.20   $263.20  
  Purchase #5 $57.72   3.467%   $59.7212   $59.72   $59.70   $59.70  
  Purchase #6 $26.32   6.467%   $28.0221   $28.02   $28.00   $28.00  
  Purchase #7 $88.51   7.650%   $95.281   $95.28   $95.30   $95.30  
  7 purchase totals = $701.15       $764.3508   $764.35   $764.35   $764.40