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 $244.91   13.482%   $277.9288   $277.93   $277.95   $277.90  
  Purchase #2 $43.30   3.374%   $44.7609   $44.76   $44.75   $44.80  
  Purchase #3 $33.27   11.680%   $37.1559   $37.16   $37.15   $37.20  
  Purchase #4 $133.82   6.713%   $142.8033   $142.80   $142.80   $142.80  
  Purchase #5 $59.54   8.833%   $64.7992   $64.80   $64.80   $64.80  
  Purchase #6 $219.88   11.114%   $244.3175   $244.32   $244.30   $244.30  
  Purchase #7 $229.52   11.628%   $256.2086   $256.21   $256.20   $256.20  
  7 purchase totals = $964.24       $1,067.9742   $1,067.98   $1,067.95   $1,068.00