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 $69.26   8.767%   $75.332   $75.33   $75.35   $75.30  
  Purchase #2 $33.82   11.369%   $37.665   $37.67   $37.65   $37.70  
  Purchase #3 $62.40   3.196%   $64.3943   $64.39   $64.40   $64.40  
  Purchase #4 $161.69   9.603%   $177.2171   $177.22   $177.20   $177.20  
  Purchase #5 $169.27   7.450%   $181.8806   $181.88   $181.90   $181.90  
  Purchase #6 $201.53   13.192%   $228.1158   $228.12   $228.10   $228.10  
  Purchase #7 $65.66   3.288%   $67.8189   $67.82   $67.80   $67.80  
  7 purchase totals = $763.63       $832.4237   $832.43   $832.40   $832.40