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 $60.85   13.391%   $68.9984   $69.00   $69.00   $69.00  
  Purchase #2 $192.87   12.742%   $217.4455   $217.45   $217.45   $217.40  
  Purchase #3 $109.75   6.165%   $116.5161   $116.52   $116.50   $116.50  
  Purchase #4 $63.52   9.768%   $69.7246   $69.72   $69.70   $69.70  
  Purchase #5 $182.31   6.392%   $193.9633   $193.96   $193.95   $194.00  
  Purchase #6 $66.94   3.315%   $69.1591   $69.16   $69.15   $69.20  
  Purchase #7 $245.97   5.457%   $259.3926   $259.39   $259.40   $259.40  
  7 purchase totals = $922.21       $995.1996   $995.20   $995.15   $995.20