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 $228.42   10.849%   $253.2013   $253.20   $253.20   $253.20  
  Purchase #2 $217.31   10.873%   $240.9381   $240.94   $240.95   $240.90  
  Purchase #3 $216.47   11.476%   $241.3121   $241.31   $241.30   $241.30  
  Purchase #4 $223.43   10.184%   $246.1841   $246.18   $246.20   $246.20  
  Purchase #5 $36.57   10.633%   $40.4585   $40.46   $40.45   $40.50  
  Purchase #6 $134.84   13.607%   $153.1877   $153.19   $153.20   $153.20  
  Purchase #7 $95.94   10.214%   $105.7393   $105.74   $105.75   $105.70  
  7 purchase totals = $1,152.98       $1,281.0211   $1,281.02   $1,281.05   $1,281.00