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 $245.53   13.612%   $278.9515   $278.95   $278.95   $279.00  
  Purchase #2 $172.27   9.115%   $187.9724   $187.97   $187.95   $188.00  
  Purchase #3 $188.90   9.695%   $207.2139   $207.21   $207.20   $207.20  
  Purchase #4 $95.58   11.367%   $106.4446   $106.44   $106.45   $106.40  
  Purchase #5 $84.47   13.170%   $95.5947   $95.59   $95.60   $95.60  
  Purchase #6 $220.98   6.288%   $234.8752   $234.88   $234.90   $234.90  
  Purchase #7 $226.56   11.740%   $253.1581   $253.16   $253.15   $253.20  
  7 purchase totals = $1,234.29       $1,364.2104   $1,364.20   $1,364.20   $1,364.30