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 $165.77   6.869%   $177.1567   $177.16   $177.15   $177.20  
  Purchase #2 $211.52   13.760%   $240.6252   $240.63   $240.65   $240.60  
  Purchase #3 $33.51   4.452%   $35.0019   $35.00   $35.00   $35.00  
  Purchase #4 $12.40   5.185%   $13.0429   $13.04   $13.05   $13.00  
  Purchase #5 $160.36   10.692%   $177.5057   $177.51   $177.50   $177.50  
  Purchase #6 $211.74   5.456%   $223.2925   $223.29   $223.30   $223.30  
  Purchase #7 $125.34   13.373%   $142.1017   $142.10   $142.10   $142.10  
  7 purchase totals = $920.64       $1,008.7266   $1,008.73   $1,008.75   $1,008.70