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 $176.72   13.751%   $201.0208   $201.02   $201.00   $201.00  
  Purchase #2 $35.43   8.309%   $38.3739   $38.37   $38.35   $38.40  
  Purchase #3 $141.85   5.633%   $149.8404   $149.84   $149.85   $149.80  
  Purchase #4 $172.52   6.265%   $183.3284   $183.33   $183.35   $183.30  
  Purchase #5 $61.64   3.840%   $64.007   $64.01   $64.00   $64.00  
  Purchase #6 $116.92   6.517%   $124.5397   $124.54   $124.55   $124.50  
  Purchase #7 $12.28   12.735%   $13.8439   $13.84   $13.85   $13.80  
  7 purchase totals = $717.36       $774.9541   $774.95   $774.95   $774.80