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   12.432%   $94.2855   $94.29   $94.30   $94.30  
  Purchase #2 $22.79   8.199%   $24.6586   $24.66   $24.65   $24.70  
  Purchase #3 $148.85   12.738%   $167.8105   $167.81   $167.80   $167.80  
  Purchase #4 $233.26   13.782%   $265.4079   $265.41   $265.40   $265.40  
  Purchase #5 $46.97   13.295%   $53.2147   $53.21   $53.20   $53.20  
  Purchase #6 $179.29   10.563%   $198.2284   $198.23   $198.25   $198.20  
  Purchase #7 $206.53   12.342%   $232.0199   $232.02   $232.00   $232.00  
  7 purchase totals = $921.55       $1,035.6255   $1,035.63   $1,035.60   $1,035.60