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 $11.32   9.137%   $12.3543   $12.35   $12.35   $12.40  
  Purchase #2 $189.74   3.856%   $197.0564   $197.06   $197.05   $197.10  
  Purchase #3 $200.49   3.188%   $206.8816   $206.88   $206.90   $206.90  
  Purchase #4 $161.55   3.733%   $167.5807   $167.58   $167.60   $167.60  
  Purchase #5 $109.55   10.458%   $121.0067   $121.01   $121.00   $121.00  
  Purchase #6 $170.25   6.872%   $181.9496   $181.95   $181.95   $181.90  
  Purchase #7 $202.78   3.269%   $209.4089   $209.41   $209.40   $209.40  
  7 purchase totals = $1,045.68       $1,096.2382   $1,096.24   $1,096.25   $1,096.30