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 $248.31   10.645%   $274.7426   $274.74   $274.75   $274.70  
  Purchase #2 $143.42   4.767%   $150.2568   $150.26   $150.25   $150.30  
  Purchase #3 $81.54   12.396%   $91.6477   $91.65   $91.65   $91.60  
  Purchase #4 $210.39   12.714%   $237.139   $237.14   $237.15   $237.10  
  Purchase #5 $244.64   3.614%   $253.4813   $253.48   $253.50   $253.50  
  Purchase #6 $165.85   11.399%   $184.7552   $184.76   $184.75   $184.80  
  Purchase #7 $143.76   12.774%   $162.1239   $162.12   $162.10   $162.10  
  7 purchase totals = $1,237.91       $1,354.1465   $1,354.15   $1,354.15   $1,354.10