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 $83.79   9.725%   $91.9386   $91.94   $91.95   $91.90  
  Purchase #2 $250.78   10.585%   $277.3251   $277.33   $277.35   $277.30  
  Purchase #3 $222.73   13.376%   $252.5224   $252.52   $252.50   $252.50  
  Purchase #4 $234.32   10.329%   $258.5229   $258.52   $258.50   $258.50  
  Purchase #5 $43.58   12.476%   $49.017   $49.02   $49.00   $49.00  
  Purchase #6 $222.75   6.433%   $237.0795   $237.08   $237.10   $237.10  
  Purchase #7 $243.37   6.442%   $259.0479   $259.05   $259.05   $259.00  
  7 purchase totals = $1,301.32       $1,425.4534   $1,425.46   $1,425.45   $1,425.30