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 $245.65   3.560%   $254.3951   $254.40   $254.40   $254.40  
  Purchase #2 $50.59   7.527%   $54.3979   $54.40   $54.40   $54.40  
  Purchase #3 $67.34   9.739%   $73.8982   $73.90   $73.90   $73.90  
  Purchase #4 $66.61   12.847%   $75.1674   $75.17   $75.15   $75.20  
  Purchase #5 $206.57   13.819%   $235.1159   $235.12   $235.10   $235.10  
  Purchase #6 $124.33   13.277%   $140.8373   $140.84   $140.85   $140.80  
  Purchase #7 $215.59   4.298%   $224.8561   $224.86   $224.85   $224.90  
  7 purchase totals = $976.68       $1,058.6679   $1,058.69   $1,058.65   $1,058.70