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 $190.33   11.261%   $211.7631   $211.76   $211.75   $211.80  
  Purchase #2 $80.52   4.158%   $83.868   $83.87   $83.85   $83.90  
  Purchase #3 $22.94   13.363%   $26.0055   $26.01   $26.00   $26.00  
  Purchase #4 $152.48   12.726%   $171.8846   $171.88   $171.90   $171.90  
  Purchase #5 $68.46   9.210%   $74.7652   $74.77   $74.75   $74.80  
  Purchase #6 $98.75   13.375%   $111.9578   $111.96   $111.95   $112.00  
  Purchase #7 $43.73   11.439%   $48.7323   $48.73   $48.75   $48.70  
  7 purchase totals = $657.21       $728.9765   $728.98   $728.95   $729.10