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 $6.64   9.222%   $7.2523   $7.25   $7.25   $7.30  
  Purchase #2 $208.25   11.434%   $232.0613   $232.06   $232.05   $232.10  
  Purchase #3 $59.66   6.658%   $63.6322   $63.63   $63.65   $63.60  
  Purchase #4 $115.49   7.549%   $124.2083   $124.21   $124.20   $124.20  
  Purchase #5 $24.94   9.868%   $27.4011   $27.40   $27.40   $27.40  
  Purchase #6 $86.95   9.219%   $94.9659   $94.97   $94.95   $95.00  
  Purchase #7 $187.51   7.810%   $202.1545   $202.15   $202.15   $202.20  
  7 purchase totals = $689.44       $751.6756   $751.67   $751.65   $751.80