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 $84.67   10.710%   $93.7382   $93.74   $93.75   $93.70  
  Purchase #2 $6.97   11.575%   $7.7768   $7.78   $7.80   $7.80  
  Purchase #3 $75.35   11.110%   $83.7214   $83.72   $83.70   $83.70  
  Purchase #4 $181.50   3.780%   $188.3607   $188.36   $188.35   $188.40  
  Purchase #5 $59.50   6.214%   $63.1973   $63.20   $63.20   $63.20  
  Purchase #6 $141.91   9.146%   $154.8891   $154.89   $154.90   $154.90  
  Purchase #7 $54.94   7.635%   $59.1347   $59.13   $59.15   $59.10  
  7 purchase totals = $604.84       $650.8182   $650.82   $650.85   $650.80