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 $58.91   7.474%   $63.3129   $63.31   $63.30   $63.30  
  Purchase #2 $229.54   13.286%   $260.0367   $260.04   $260.05   $260.00  
  Purchase #3 $33.56   7.392%   $36.0408   $36.04   $36.05   $36.00  
  Purchase #4 $157.50   13.332%   $178.4979   $178.50   $178.50   $178.50  
  Purchase #5 $212.57   13.859%   $242.0301   $242.03   $242.05   $242.00  
  Purchase #6 $157.73   10.621%   $174.4825   $174.48   $174.50   $174.50  
  Purchase #7 $244.52   8.306%   $264.8298   $264.83   $264.85   $264.80  
  7 purchase totals = $1,094.33       $1,219.2307   $1,219.23   $1,219.30   $1,219.10