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 $145.52   12.632%   $163.9021   $163.90   $163.90   $163.90  
  Purchase #2 $75.58   9.277%   $82.5916   $82.59   $82.60   $82.60  
  Purchase #3 $24.78   10.187%   $27.3043   $27.30   $27.30   $27.30  
  Purchase #4 $134.88   5.851%   $142.7718   $142.77   $142.75   $142.80  
  Purchase #5 $165.77   12.784%   $186.962   $186.96   $186.95   $187.00  
  Purchase #6 $204.83   11.607%   $228.6046   $228.60   $228.60   $228.60  
  Purchase #7 $120.26   13.307%   $136.263   $136.26   $136.25   $136.30  
  7 purchase totals = $871.62       $968.3994   $968.38   $968.35   $968.50