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 $225.98   7.222%   $242.3003   $242.30   $242.30   $242.30  
  Purchase #2 $159.78   6.173%   $169.6432   $169.64   $169.65   $169.60  
  Purchase #3 $59.46   5.812%   $62.9158   $62.92   $62.90   $62.90  
  Purchase #4 $8.79   3.707%   $9.1158   $9.12   $9.10   $9.10  
  Purchase #5 $210.70   9.493%   $230.7018   $230.70   $230.70   $230.70  
  Purchase #6 $189.27   3.442%   $195.7847   $195.78   $195.80   $195.80  
  Purchase #7 $216.31   9.567%   $237.0044   $237.00   $237.00   $237.00  
  7 purchase totals = $1,070.29       $1,147.4660   $1,147.46   $1,147.45   $1,147.40