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 $48.28   12.301%   $54.2189   $54.22   $54.20   $54.20  
  Purchase #2 $235.32   4.669%   $246.3071   $246.31   $246.30   $246.30  
  Purchase #3 $136.88   12.205%   $153.5862   $153.59   $153.60   $153.60  
  Purchase #4 $189.39   3.241%   $195.5281   $195.53   $195.55   $195.50  
  Purchase #5 $232.39   5.274%   $244.6462   $244.65   $244.65   $244.60  
  Purchase #6 $243.45   13.592%   $276.5397   $276.54   $276.55   $276.50  
  Purchase #7 $171.69   11.772%   $191.9013   $191.90   $191.90   $191.90  
  7 purchase totals = $1,257.40       $1,362.7275   $1,362.74   $1,362.75   $1,362.60