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 $158.96   11.786%   $177.695   $177.70   $177.70   $177.70  
  Purchase #2 $67.67   8.283%   $73.2751   $73.28   $73.30   $73.30  
  Purchase #3 $150.69   13.572%   $171.1416   $171.14   $171.15   $171.10  
  Purchase #4 $216.60   13.675%   $246.2201   $246.22   $246.20   $246.20  
  Purchase #5 $163.68   10.403%   $180.7076   $180.71   $180.70   $180.70  
  Purchase #6 $96.32   10.809%   $106.7312   $106.73   $106.75   $106.70  
  Purchase #7 $203.98   12.242%   $228.9512   $228.95   $228.95   $229.00  
  7 purchase totals = $1,057.90       $1,184.7218   $1,184.73   $1,184.75   $1,184.70