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 $81.31   13.570%   $92.3438   $92.34   $92.35   $92.30  
  Purchase #2 $123.86   11.467%   $138.063   $138.06   $138.05   $138.10  
  Purchase #3 $228.87   11.813%   $255.9064   $255.91   $255.90   $255.90  
  Purchase #4 $144.94   6.239%   $153.9828   $153.98   $154.00   $154.00  
  Purchase #5 $58.54   7.462%   $62.9083   $62.91   $62.90   $62.90  
  Purchase #6 $41.87   4.365%   $43.6976   $43.70   $43.70   $43.70  
  Purchase #7 $135.51   9.237%   $148.0271   $148.03   $148.05   $148.00  
  7 purchase totals = $814.90       $894.9290   $894.93   $894.95   $894.90