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 $173.56   6.184%   $184.293   $184.29   $184.30   $184.30  
  Purchase #2 $228.79   6.339%   $243.293   $243.29   $243.30   $243.30  
  Purchase #3 $158.91   11.513%   $177.2053   $177.21   $177.20   $177.20  
  Purchase #4 $54.68   13.628%   $62.1318   $62.13   $62.15   $62.10  
  Purchase #5 $151.85   5.694%   $160.4963   $160.50   $160.50   $160.50  
  Purchase #6 $226.72   13.180%   $256.6017   $256.60   $256.60   $256.60  
  Purchase #7 $147.56   6.219%   $156.7368   $156.74   $156.75   $156.70  
  7 purchase totals = $1,142.07       $1,240.7579   $1,240.76   $1,240.80   $1,240.70