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 $183.50   6.519%   $195.4624   $195.46   $195.45   $195.50  
  Purchase #2 $185.56   9.198%   $202.6278   $202.63   $202.65   $202.60  
  Purchase #3 $72.96   8.132%   $78.8931   $78.89   $78.90   $78.90  
  Purchase #4 $211.67   9.804%   $232.4221   $232.42   $232.40   $232.40  
  Purchase #5 $45.74   7.851%   $49.331   $49.33   $49.35   $49.30  
  Purchase #6 $30.90   4.438%   $32.2713   $32.27   $32.25   $32.30  
  Purchase #7 $194.84   3.286%   $201.2424   $201.24   $201.25   $201.20  
  7 purchase totals = $925.17       $992.2501   $992.24   $992.25   $992.20