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 $62.52   4.148%   $65.1133   $65.11   $65.10   $65.10  
  Purchase #2 $97.92   10.618%   $108.3171   $108.32   $108.30   $108.30  
  Purchase #3 $126.62   7.616%   $136.2634   $136.26   $136.25   $136.30  
  Purchase #4 $20.42   12.318%   $22.9353   $22.94   $22.95   $22.90  
  Purchase #5 $196.79   5.482%   $207.578   $207.58   $207.60   $207.60  
  Purchase #6 $179.28   7.825%   $193.3087   $193.31   $193.30   $193.30  
  Purchase #7 $29.30   8.460%   $31.7788   $31.78   $31.80   $31.80  
  7 purchase totals = $712.85       $765.2946   $765.30   $765.30   $765.30