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 $163.27   10.846%   $180.9783   $180.98   $181.00   $181.00  
  Purchase #2 $235.97   3.393%   $243.9765   $243.98   $244.00   $244.00  
  Purchase #3 $104.30   8.865%   $113.5462   $113.55   $113.55   $113.50  
  Purchase #4 $158.35   7.655%   $170.4717   $170.47   $170.45   $170.50  
  Purchase #5 $111.76   8.769%   $121.5602   $121.56   $121.55   $121.60  
  Purchase #6 $248.65   9.359%   $271.9212   $271.92   $271.90   $271.90  
  Purchase #7 $67.34   9.407%   $73.6747   $73.67   $73.65   $73.70  
  7 purchase totals = $1,089.64       $1,176.1288   $1,176.13   $1,176.10   $1,176.20