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 $58.65   11.713%   $65.5197   $65.52   $65.50   $65.50  
  Purchase #2 $37.87   7.349%   $40.6531   $40.65   $40.65   $40.70  
  Purchase #3 $38.31   6.493%   $40.7975   $40.80   $40.80   $40.80  
  Purchase #4 $88.42   10.841%   $98.0056   $98.01   $98.00   $98.00  
  Purchase #5 $135.99   7.854%   $146.6707   $146.67   $146.65   $146.70  
  Purchase #6 $147.95   7.555%   $159.1276   $159.13   $159.15   $159.10  
  Purchase #7 $226.83   7.355%   $243.5133   $243.51   $243.50   $243.50  
  7 purchase totals = $734.02       $794.2875   $794.29   $794.25   $794.30