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 $49.71   10.167%   $54.764   $54.76   $54.75   $54.80  
  Purchase #2 $70.86   3.184%   $73.1162   $73.12   $73.10   $73.10  
  Purchase #3 $103.56   7.857%   $111.6967   $111.70   $111.70   $111.70  
  Purchase #4 $190.42   13.475%   $216.0791   $216.08   $216.10   $216.10  
  Purchase #5 $7.38   13.256%   $8.3583   $8.36   $8.35   $8.40  
  Purchase #6 $68.75   8.231%   $74.4088   $74.41   $74.40   $74.40  
  Purchase #7 $145.77   11.624%   $162.7143   $162.71   $162.70   $162.70  
  7 purchase totals = $636.45       $701.1374   $701.14   $701.10   $701.20