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 $142.68   6.328%   $151.7088   $151.71   $151.70   $151.70  
  Purchase #2 $177.89   9.162%   $194.1883   $194.19   $194.20   $194.20  
  Purchase #3 $46.72   9.387%   $51.1056   $51.11   $51.10   $51.10  
  Purchase #4 $240.67   3.392%   $248.8335   $248.83   $248.85   $248.80  
  Purchase #5 $110.96   6.653%   $118.3422   $118.34   $118.35   $118.30  
  Purchase #6 $36.83   6.239%   $39.1278   $39.13   $39.15   $39.10  
  Purchase #7 $191.77   5.544%   $202.4017   $202.40   $202.40   $202.40  
  7 purchase totals = $947.52       $1,005.7079   $1,005.71   $1,005.75   $1,005.60