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 $187.72   8.651%   $203.9597   $203.96   $203.95   $204.00  
  Purchase #2 $40.59   6.749%   $43.3294   $43.33   $43.35   $43.30  
  Purchase #3 $119.76   13.239%   $135.615   $135.62   $135.60   $135.60  
  Purchase #4 $102.34   8.651%   $111.1934   $111.19   $111.20   $111.20  
  Purchase #5 $215.75   13.563%   $245.0122   $245.01   $245.00   $245.00  
  Purchase #6 $62.90   5.372%   $66.279   $66.28   $66.30   $66.30  
  Purchase #7 $39.96   4.616%   $41.8046   $41.80   $41.80   $41.80  
  7 purchase totals = $769.02       $847.1933   $847.19   $847.20   $847.20