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 $68.41   9.585%   $74.9671   $74.97   $74.95   $75.00  
  Purchase #2 $189.83   13.282%   $215.0432   $215.04   $215.05   $215.00  
  Purchase #3 $208.41   9.790%   $228.8133   $228.81   $228.80   $228.80  
  Purchase #4 $95.47   13.586%   $108.4406   $108.44   $108.45   $108.40  
  Purchase #5 $5.55   7.343%   $5.9575   $5.96   $5.95   $6.00  
  Purchase #6 $150.70   7.729%   $162.3476   $162.35   $162.35   $162.30  
  Purchase #7 $193.43   12.620%   $217.8409   $217.84   $217.85   $217.80  
  7 purchase totals = $911.80       $1,013.4102   $1,013.41   $1,013.40   $1,013.30