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 $141.62   13.874%   $161.2684   $161.27   $161.25   $161.30  
  Purchase #2 $63.49   12.453%   $71.3964   $71.40   $71.40   $71.40  
  Purchase #3 $242.52   6.575%   $258.4657   $258.47   $258.45   $258.50  
  Purchase #4 $135.29   8.642%   $146.9818   $146.98   $147.00   $147.00  
  Purchase #5 $155.28   6.263%   $165.0052   $165.01   $165.00   $165.00  
  Purchase #6 $79.34   9.290%   $86.7107   $86.71   $86.70   $86.70  
  Purchase #7 $34.80   6.194%   $36.9555   $36.96   $36.95   $37.00  
  7 purchase totals = $852.34       $926.7837   $926.80   $926.75   $926.90