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 $242.96   8.569%   $263.7792   $263.78   $263.80   $263.80  
  Purchase #2 $148.71   9.718%   $163.1616   $163.16   $163.15   $163.20  
  Purchase #3 $194.74   4.472%   $203.4488   $203.45   $203.45   $203.40  
  Purchase #4 $188.98   6.764%   $201.7626   $201.76   $201.75   $201.80  
  Purchase #5 $73.57   12.839%   $83.0157   $83.02   $83.00   $83.00  
  Purchase #6 $86.94   5.139%   $91.4078   $91.41   $91.40   $91.40  
  Purchase #7 $31.70   10.350%   $34.981   $34.98   $35.00   $35.00  
  7 purchase totals = $967.60       $1,041.5567   $1,041.56   $1,041.55   $1,041.60