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 $91.96   10.693%   $101.7933   $101.79   $101.80   $101.80  
  Purchase #2 $59.79   9.242%   $65.3158   $65.32   $65.30   $65.30  
  Purchase #3 $167.67   8.414%   $181.7778   $181.78   $181.80   $181.80  
  Purchase #4 $230.29   4.235%   $240.0428   $240.04   $240.05   $240.00  
  Purchase #5 $204.36   12.784%   $230.4854   $230.49   $230.50   $230.50  
  Purchase #6 $180.50   4.282%   $188.229   $188.23   $188.25   $188.20  
  Purchase #7 $229.60   12.429%   $258.137   $258.14   $258.15   $258.10  
  7 purchase totals = $1,164.17       $1,265.7811   $1,265.79   $1,265.85   $1,265.70