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 $66.65   13.755%   $75.8177   $75.82   $75.80   $75.80  
  Purchase #2 $211.27   11.479%   $235.5217   $235.52   $235.50   $235.50  
  Purchase #3 $30.74   13.241%   $34.8103   $34.81   $34.80   $34.80  
  Purchase #4 $169.86   4.742%   $177.9148   $177.91   $177.90   $177.90  
  Purchase #5 $92.33   6.689%   $98.506   $98.51   $98.50   $98.50  
  Purchase #6 $126.51   4.139%   $131.7462   $131.75   $131.75   $131.70  
  Purchase #7 $43.34   4.341%   $45.2214   $45.22   $45.20   $45.20  
  7 purchase totals = $740.70       $799.5381   $799.54   $799.45   $799.40