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 $46.58   7.817%   $50.2212   $50.22   $50.20   $50.20  
  Purchase #2 $84.27   8.443%   $91.3849   $91.38   $91.40   $91.40  
  Purchase #3 $102.33   8.371%   $110.896   $110.90   $110.90   $110.90  
  Purchase #4 $196.52   3.636%   $203.6655   $203.67   $203.65   $203.70  
  Purchase #5 $163.77   12.499%   $184.2396   $184.24   $184.25   $184.20  
  Purchase #6 $163.64   4.216%   $170.5391   $170.54   $170.55   $170.50  
  Purchase #7 $240.49   7.674%   $258.9452   $258.95   $258.95   $258.90  
  7 purchase totals = $997.60       $1,069.8915   $1,069.90   $1,069.90   $1,069.80