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 $245.82   8.168%   $265.8986   $265.90   $265.90   $265.90  
  Purchase #2 $77.79   6.230%   $82.6363   $82.64   $82.65   $82.60  
  Purchase #3 $81.58   11.754%   $91.1689   $91.17   $91.15   $91.20  
  Purchase #4 $160.46   9.386%   $175.5208   $175.52   $175.50   $175.50  
  Purchase #5 $149.94   3.336%   $154.942   $154.94   $154.95   $154.90  
  Purchase #6 $173.95   8.448%   $188.6453   $188.65   $188.65   $188.60  
  Purchase #7 $194.65   13.750%   $221.4144   $221.41   $221.40   $221.40  
  7 purchase totals = $1,084.19       $1,180.2263   $1,180.23   $1,180.20   $1,180.10