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 $46.77   13.346%   $53.0119   $53.01   $53.00   $53.00  
  Purchase #2 $74.79   6.320%   $79.5167   $79.52   $79.50   $79.50  
  Purchase #3 $92.59   11.195%   $102.9555   $102.96   $102.95   $103.00  
  Purchase #4 $165.85   5.413%   $174.8275   $174.83   $174.85   $174.80  
  Purchase #5 $162.90   4.541%   $170.2973   $170.30   $170.30   $170.30  
  Purchase #6 $40.56   13.722%   $46.1256   $46.13   $46.15   $46.10  
  Purchase #7 $103.58   5.731%   $109.5162   $109.52   $109.50   $109.50  
  7 purchase totals = $687.04       $736.2507   $736.27   $736.25   $736.20