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 $160.83   10.244%   $177.3054   $177.31   $177.30   $177.30  
  Purchase #2 $59.93   11.400%   $66.762   $66.76   $66.75   $66.80  
  Purchase #3 $179.92   7.816%   $193.9825   $193.98   $194.00   $194.00  
  Purchase #4 $49.31   3.741%   $51.1547   $51.15   $51.15   $51.20  
  Purchase #5 $36.40   13.487%   $41.3093   $41.31   $41.30   $41.30  
  Purchase #6 $172.46   7.156%   $184.8012   $184.80   $184.80   $184.80  
  Purchase #7 $145.33   4.318%   $151.6053   $151.61   $151.60   $151.60  
  7 purchase totals = $804.18       $866.9204   $866.92   $866.90   $867.00