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 $80.82   13.533%   $91.7574   $91.76   $91.75   $91.80  
  Purchase #2 $83.52   13.185%   $94.5321   $94.53   $94.55   $94.50  
  Purchase #3 $238.61   10.200%   $262.9482   $262.95   $262.95   $262.90  
  Purchase #4 $87.47   8.243%   $94.6802   $94.68   $94.70   $94.70  
  Purchase #5 $130.40   3.428%   $134.8701   $134.87   $134.85   $134.90  
  Purchase #6 $238.43   12.530%   $268.3053   $268.31   $268.30   $268.30  
  Purchase #7 $107.48   5.332%   $113.2108   $113.21   $113.20   $113.20  
  7 purchase totals = $966.73       $1,060.3041   $1,060.31   $1,060.30   $1,060.30