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 $84.62   11.752%   $94.5645   $94.56   $94.55   $94.60  
  Purchase #2 $188.58   6.592%   $201.0112   $201.01   $201.00   $201.00  
  Purchase #3 $122.84   10.207%   $135.3783   $135.38   $135.40   $135.40  
  Purchase #4 $57.37   11.283%   $63.8431   $63.84   $63.85   $63.80  
  Purchase #5 $194.56   4.628%   $203.5642   $203.56   $203.55   $203.60  
  Purchase #6 $92.55   4.354%   $96.5796   $96.58   $96.60   $96.60  
  Purchase #7 $246.30   13.357%   $279.1983   $279.20   $279.20   $279.20  
  7 purchase totals = $986.82       $1,074.1392   $1,074.13   $1,074.15   $1,074.20