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 $54.56   6.662%   $58.1948   $58.19   $58.20   $58.20  
  Purchase #2 $158.89   8.591%   $172.5402   $172.54   $172.55   $172.50  
  Purchase #3 $147.48   5.561%   $155.6814   $155.68   $155.70   $155.70  
  Purchase #4 $205.56   12.216%   $230.6712   $230.67   $230.65   $230.70  
  Purchase #5 $212.57   6.754%   $226.927   $226.93   $226.95   $226.90  
  Purchase #6 $110.63   11.195%   $123.015   $123.02   $123.00   $123.00  
  Purchase #7 $51.76   8.630%   $56.2269   $56.23   $56.25   $56.20  
  7 purchase totals = $941.45       $1,023.2565   $1,023.26   $1,023.30   $1,023.20