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 $231.52   5.759%   $244.8532   $244.85   $244.85   $244.90  
  Purchase #2 $113.38   5.561%   $119.6851   $119.69   $119.70   $119.70  
  Purchase #3 $123.42   8.395%   $133.7811   $133.78   $133.80   $133.80  
  Purchase #4 $193.53   9.145%   $211.2283   $211.23   $211.25   $211.20  
  Purchase #5 $48.86   5.798%   $51.6929   $51.69   $51.70   $51.70  
  Purchase #6 $204.56   7.499%   $219.9   $219.90   $219.90   $219.90  
  Purchase #7 $65.49   5.299%   $68.9603   $68.96   $68.95   $69.00  
  7 purchase totals = $980.76       $1,050.1009   $1,050.10   $1,050.15   $1,050.20