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 $150.78   9.442%   $165.0166   $165.02   $165.00   $165.00  
  Purchase #2 $117.56   12.873%   $132.6935   $132.69   $132.70   $132.70  
  Purchase #3 $64.32   12.740%   $72.5144   $72.51   $72.50   $72.50  
  Purchase #4 $87.57   10.363%   $96.6449   $96.64   $96.65   $96.60  
  Purchase #5 $61.64   6.318%   $65.5344   $65.53   $65.55   $65.50  
  Purchase #6 $205.41   13.336%   $232.8035   $232.80   $232.80   $232.80  
  Purchase #7 $26.78   5.655%   $28.2944   $28.29   $28.30   $28.30  
  7 purchase totals = $714.06       $793.5017   $793.48   $793.50   $793.40