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 $91.69   11.274%   $102.0271   $102.03   $102.05   $102.00  
  Purchase #2 $212.80   9.397%   $232.7968   $232.80   $232.80   $232.80  
  Purchase #3 $36.87   12.358%   $41.4264   $41.43   $41.45   $41.40  
  Purchase #4 $183.40   3.283%   $189.421   $189.42   $189.40   $189.40  
  Purchase #5 $95.81   9.250%   $104.6724   $104.67   $104.65   $104.70  
  Purchase #6 $150.90   11.722%   $168.5885   $168.59   $168.60   $168.60  
  Purchase #7 $14.26   5.182%   $14.999   $15.00   $15.00   $15.00  
  7 purchase totals = $785.73       $853.9312   $853.94   $853.95   $853.90