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 $35.65   4.662%   $37.312   $37.31   $37.30   $37.30  
  Purchase #2 $117.33   13.564%   $133.2446   $133.24   $133.25   $133.20  
  Purchase #3 $122.37   10.384%   $135.0769   $135.08   $135.10   $135.10  
  Purchase #4 $60.38   7.637%   $64.9912   $64.99   $65.00   $65.00  
  Purchase #5 $188.98   7.840%   $203.796   $203.80   $203.80   $203.80  
  Purchase #6 $38.54   13.456%   $43.7259   $43.73   $43.75   $43.70  
  Purchase #7 $128.28   11.795%   $143.4106   $143.41   $143.40   $143.40  
  7 purchase totals = $691.53       $761.5572   $761.56   $761.60   $761.50