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 $31.26   8.419%   $33.8918   $33.89   $33.90   $33.90  
  Purchase #2 $202.97   3.382%   $209.8344   $209.83   $209.85   $209.80  
  Purchase #3 $135.84   7.286%   $145.7373   $145.74   $145.75   $145.70  
  Purchase #4 $132.91   3.305%   $137.3027   $137.30   $137.30   $137.30  
  Purchase #5 $24.93   11.475%   $27.7907   $27.79   $27.80   $27.80  
  Purchase #6 $140.65   10.342%   $155.196   $155.20   $155.20   $155.20  
  Purchase #7 $219.98   10.691%   $243.4981   $243.50   $243.50   $243.50  
  7 purchase totals = $888.54       $953.2510   $953.25   $953.30   $953.20