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 $82.27   12.236%   $92.3366   $92.34   $92.35   $92.30  
  Purchase #2 $141.47   9.444%   $154.8304   $154.83   $154.85   $154.80  
  Purchase #3 $21.89   13.390%   $24.8211   $24.82   $24.80   $24.80  
  Purchase #4 $56.33   3.801%   $58.4711   $58.47   $58.45   $58.50  
  Purchase #5 $140.64   5.203%   $147.9575   $147.96   $147.95   $148.00  
  Purchase #6 $181.26   6.867%   $193.7071   $193.71   $193.70   $193.70  
  Purchase #7 $68.97   9.315%   $75.3946   $75.39   $75.40   $75.40  
  7 purchase totals = $692.83       $747.5184   $747.52   $747.50   $747.50