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 $67.61   5.854%   $71.5679   $71.57   $71.55   $71.60  
  Purchase #2 $81.54   6.718%   $87.0179   $87.02   $87.00   $87.00  
  Purchase #3 $239.82   8.674%   $260.622   $260.62   $260.60   $260.60  
  Purchase #4 $81.49   3.562%   $84.3927   $84.39   $84.40   $84.40  
  Purchase #5 $154.87   8.284%   $167.6994   $167.70   $167.70   $167.70  
  Purchase #6 $179.79   4.855%   $188.5188   $188.52   $188.50   $188.50  
  Purchase #7 $135.66   13.521%   $154.0026   $154.00   $154.00   $154.00  
  7 purchase totals = $940.78       $1,013.8213   $1,013.82   $1,013.75   $1,013.80