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 $57.42   9.474%   $62.86   $62.86   $62.85   $62.90  
  Purchase #2 $191.27   6.644%   $203.978   $203.98   $204.00   $204.00  
  Purchase #3 $175.71   7.455%   $188.8092   $188.81   $188.80   $188.80  
  Purchase #4 $240.68   8.368%   $260.8201   $260.82   $260.80   $260.80  
  Purchase #5 $159.97   4.659%   $167.423   $167.42   $167.40   $167.40  
  Purchase #6 $23.29   11.368%   $25.9376   $25.94   $25.95   $25.90  
  Purchase #7 $142.25   4.543%   $148.7124   $148.71   $148.70   $148.70  
  7 purchase totals = $990.59       $1,058.5403   $1,058.54   $1,058.50   $1,058.50