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 $242.49   13.282%   $274.6975   $274.70   $274.70   $274.70  
  Purchase #2 $115.43   9.382%   $126.2596   $126.26   $126.25   $126.30  
  Purchase #3 $160.64   7.396%   $172.5209   $172.52   $172.50   $172.50  
  Purchase #4 $223.68   7.535%   $240.5343   $240.53   $240.55   $240.50  
  Purchase #5 $115.79   12.217%   $129.9361   $129.94   $129.95   $129.90  
  Purchase #6 $41.36   13.833%   $47.0813   $47.08   $47.10   $47.10  
  Purchase #7 $66.60   11.339%   $74.1518   $74.15   $74.15   $74.20  
  7 purchase totals = $965.99       $1,065.1815   $1,065.18   $1,065.20   $1,065.20