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 $186.27   10.580%   $205.9774   $205.98   $206.00   $206.00  
  Purchase #2 $81.74   12.308%   $91.8006   $91.80   $91.80   $91.80  
  Purchase #3 $214.43   10.304%   $236.5249   $236.52   $236.50   $236.50  
  Purchase #4 $40.72   9.355%   $44.5294   $44.53   $44.55   $44.50  
  Purchase #5 $247.87   8.733%   $269.5165   $269.52   $269.50   $269.50  
  Purchase #6 $169.53   4.433%   $177.0453   $177.05   $177.05   $177.00  
  Purchase #7 $185.61   9.311%   $202.8921   $202.89   $202.90   $202.90  
  7 purchase totals = $1,126.17       $1,228.2862   $1,228.29   $1,228.30   $1,228.20