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 $211.26   8.535%   $229.291   $229.29   $229.30   $229.30  
  Purchase #2 $245.31   13.133%   $277.5266   $277.53   $277.55   $277.50  
  Purchase #3 $202.52   11.532%   $225.8746   $225.87   $225.85   $225.90  
  Purchase #4 $14.45   8.844%   $15.728   $15.73   $15.75   $15.70  
  Purchase #5 $248.51   4.236%   $259.0369   $259.04   $259.05   $259.00  
  Purchase #6 $206.56   13.843%   $235.1541   $235.15   $235.15   $235.20  
  Purchase #7 $133.40   12.795%   $150.4685   $150.47   $150.45   $150.50  
  7 purchase totals = $1,262.01       $1,393.0797   $1,393.08   $1,393.10   $1,393.10