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 $243.79   13.390%   $276.4335   $276.43   $276.45   $276.40  
  Purchase #2 $69.45   7.148%   $74.4143   $74.41   $74.40   $74.40  
  Purchase #3 $26.58   9.835%   $29.1941   $29.19   $29.20   $29.20  
  Purchase #4 $40.94   13.755%   $46.5713   $46.57   $46.55   $46.60  
  Purchase #5 $184.53   3.303%   $190.625   $190.63   $190.65   $190.60  
  Purchase #6 $213.39   3.670%   $221.2214   $221.22   $221.20   $221.20  
  Purchase #7 $219.63   4.669%   $229.8845   $229.88   $229.90   $229.90  
  7 purchase totals = $998.31       $1,068.3441   $1,068.33   $1,068.35   $1,068.30