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 $22.85   13.760%   $25.9942   $25.99   $26.00   $26.00  
  Purchase #2 $67.45   12.361%   $75.7875   $75.79   $75.80   $75.80  
  Purchase #3 $222.46   7.586%   $239.3358   $239.34   $239.35   $239.30  
  Purchase #4 $187.57   8.662%   $203.8173   $203.82   $203.80   $203.80  
  Purchase #5 $44.86   7.324%   $48.1455   $48.15   $48.15   $48.10  
  Purchase #6 $184.55   5.815%   $195.2816   $195.28   $195.30   $195.30  
  Purchase #7 $225.91   9.331%   $246.9897   $246.99   $247.00   $247.00  
  7 purchase totals = $955.65       $1,035.3516   $1,035.36   $1,035.40   $1,035.30