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 $50.53   11.537%   $56.3596   $56.36   $56.35   $56.40  
  Purchase #2 $40.95   5.316%   $43.1269   $43.13   $43.15   $43.10  
  Purchase #3 $68.88   4.224%   $71.7895   $71.79   $71.80   $71.80  
  Purchase #4 $207.54   6.440%   $220.9056   $220.91   $220.90   $220.90  
  Purchase #5 $193.60   13.392%   $219.5269   $219.53   $219.55   $219.50  
  Purchase #6 $211.25   5.708%   $223.3082   $223.31   $223.30   $223.30  
  Purchase #7 $182.26   3.432%   $188.5152   $188.52   $188.50   $188.50  
  7 purchase totals = $955.01       $1,023.5319   $1,023.55   $1,023.55   $1,023.50