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 $91.26   7.794%   $98.3728   $98.37   $98.35   $98.40  
  Purchase #2 $26.87   10.158%   $29.5995   $29.60   $29.60   $29.60  
  Purchase #3 $166.33   12.787%   $187.5986   $187.60   $187.60   $187.60  
  Purchase #4 $219.43   3.381%   $226.8489   $226.85   $226.85   $226.80  
  Purchase #5 $40.45   10.701%   $44.7786   $44.78   $44.80   $44.80  
  Purchase #6 $99.90   7.302%   $107.1947   $107.19   $107.20   $107.20  
  Purchase #7 $58.75   3.520%   $60.818   $60.82   $60.80   $60.80  
  7 purchase totals = $702.99       $755.2111   $755.21   $755.20   $755.20