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 $181.49   8.834%   $197.5228   $197.52   $197.50   $197.50  
  Purchase #2 $63.43   11.203%   $70.5361   $70.54   $70.55   $70.50  
  Purchase #3 $67.80   9.410%   $74.18   $74.18   $74.20   $74.20  
  Purchase #4 $150.57   11.548%   $167.9578   $167.96   $167.95   $168.00  
  Purchase #5 $202.36   6.195%   $214.8962   $214.90   $214.90   $214.90  
  Purchase #6 $239.56   4.515%   $250.3761   $250.38   $250.40   $250.40  
  Purchase #7 $101.53   3.155%   $104.7333   $104.73   $104.75   $104.70  
  7 purchase totals = $1,006.74       $1,080.2023   $1,080.21   $1,080.25   $1,080.20