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 $215.35   10.699%   $238.3903   $238.39   $238.40   $238.40  
  Purchase #2 $33.38   8.326%   $36.1592   $36.16   $36.15   $36.20  
  Purchase #3 $92.70   12.707%   $104.4794   $104.48   $104.50   $104.50  
  Purchase #4 $150.73   11.180%   $167.5816   $167.58   $167.60   $167.60  
  Purchase #5 $184.29   12.764%   $207.8128   $207.81   $207.80   $207.80  
  Purchase #6 $39.38   11.158%   $43.774   $43.77   $43.75   $43.80  
  Purchase #7 $216.47   13.525%   $245.7476   $245.75   $245.75   $245.70  
  7 purchase totals = $932.30       $1,043.9449   $1,043.94   $1,043.95   $1,044.00