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 $223.97   10.733%   $248.0087   $248.01   $248.00   $248.00  
  Purchase #2 $39.38   4.646%   $41.2096   $41.21   $41.20   $41.20  
  Purchase #3 $151.92   8.497%   $164.8286   $164.83   $164.85   $164.80  
  Purchase #4 $202.99   4.740%   $212.6117   $212.61   $212.60   $212.60  
  Purchase #5 $147.33   4.229%   $153.5606   $153.56   $153.55   $153.60  
  Purchase #6 $52.87   6.764%   $56.4461   $56.45   $56.45   $56.40  
  Purchase #7 $164.91   3.812%   $171.1964   $171.20   $171.20   $171.20  
  7 purchase totals = $983.37       $1,047.8617   $1,047.87   $1,047.85   $1,047.80