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 $224.78   5.621%   $237.4149   $237.41   $237.40   $237.40  
  Purchase #2 $175.43   4.435%   $183.2103   $183.21   $183.20   $183.20  
  Purchase #3 $89.52   3.800%   $92.9218   $92.92   $92.90   $92.90  
  Purchase #4 $11.61   5.123%   $12.2048   $12.20   $12.20   $12.20  
  Purchase #5 $179.75   13.324%   $203.6999   $203.70   $203.70   $203.70  
  Purchase #6 $207.29   5.782%   $219.2755   $219.28   $219.30   $219.30  
  Purchase #7 $52.43   4.729%   $54.9094   $54.91   $54.90   $54.90  
  7 purchase totals = $940.81       $1,003.6366   $1,003.63   $1,003.60   $1,003.60