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 $83.86   10.735%   $92.8624   $92.86   $92.85   $92.90  
  Purchase #2 $247.78   6.199%   $263.1399   $263.14   $263.15   $263.10  
  Purchase #3 $226.29   9.413%   $247.5907   $247.59   $247.60   $247.60  
  Purchase #4 $125.71   7.815%   $135.5342   $135.53   $135.55   $135.50  
  Purchase #5 $103.81   4.736%   $108.7264   $108.73   $108.75   $108.70  
  Purchase #6 $167.57   8.575%   $181.9391   $181.94   $181.95   $181.90  
  Purchase #7 $40.52   9.105%   $44.2093   $44.21   $44.20   $44.20  
  7 purchase totals = $995.54       $1,074.0020   $1,074.00   $1,074.05   $1,073.90