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 $247.63   11.621%   $276.4071   $276.41   $276.40   $276.40  
  Purchase #2 $221.61   5.871%   $234.6207   $234.62   $234.60   $234.60  
  Purchase #3 $50.29   10.479%   $55.5599   $55.56   $55.55   $55.60  
  Purchase #4 $35.68   3.642%   $36.9795   $36.98   $37.00   $37.00  
  Purchase #5 $120.74   6.847%   $129.0071   $129.01   $129.00   $129.00  
  Purchase #6 $230.61   10.151%   $254.0192   $254.02   $254.00   $254.00  
  Purchase #7 $151.44   10.798%   $167.7925   $167.79   $167.80   $167.80  
  7 purchase totals = $1,058.00       $1,154.3860   $1,154.39   $1,154.35   $1,154.40