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 $235.84   7.405%   $253.304   $253.30   $253.30   $253.30  
  Purchase #2 $14.45   6.117%   $15.3339   $15.33   $15.35   $15.30  
  Purchase #3 $47.89   12.709%   $53.9763   $53.98   $54.00   $54.00  
  Purchase #4 $184.41   6.382%   $196.179   $196.18   $196.20   $196.20  
  Purchase #5 $83.35   12.450%   $93.7271   $93.73   $93.75   $93.70  
  Purchase #6 $202.45   7.510%   $217.654   $217.65   $217.65   $217.70  
  Purchase #7 $149.94   7.498%   $161.1825   $161.18   $161.20   $161.20  
  7 purchase totals = $918.33       $991.3568   $991.35   $991.45   $991.40