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 $189.73   13.185%   $214.7459   $214.75   $214.75   $214.70  
  Purchase #2 $80.29   13.290%   $90.9605   $90.96   $90.95   $91.00  
  Purchase #3 $69.74   6.739%   $74.4398   $74.44   $74.45   $74.40  
  Purchase #4 $103.87   6.693%   $110.822   $110.82   $110.80   $110.80  
  Purchase #5 $49.62   5.593%   $52.3952   $52.40   $52.40   $52.40  
  Purchase #6 $204.53   11.111%   $227.2553   $227.26   $227.25   $227.30  
  Purchase #7 $223.74   6.160%   $237.5224   $237.52   $237.50   $237.50  
  7 purchase totals = $921.52       $1,008.1411   $1,008.15   $1,008.10   $1,008.10