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 $244.76   3.566%   $253.4881   $253.49   $253.50   $253.50  
  Purchase #2 $52.64   8.366%   $57.0439   $57.04   $57.05   $57.00  
  Purchase #3 $191.99   3.833%   $199.349   $199.35   $199.35   $199.30  
  Purchase #4 $29.89   10.561%   $33.0467   $33.05   $33.05   $33.00  
  Purchase #5 $67.32   9.261%   $73.5545   $73.55   $73.55   $73.60  
  Purchase #6 $201.39   5.182%   $211.826   $211.83   $211.85   $211.80  
  Purchase #7 $188.29   3.311%   $194.5243   $194.52   $194.50   $194.50  
  7 purchase totals = $976.28       $1,022.8325   $1,022.83   $1,022.85   $1,022.70