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 $243.41   8.240%   $263.467   $263.47   $263.45   $263.50  
  Purchase #2 $84.64   9.393%   $92.5902   $92.59   $92.60   $92.60  
  Purchase #3 $125.27   9.630%   $137.3335   $137.33   $137.35   $137.30  
  Purchase #4 $105.66   4.701%   $110.6271   $110.63   $110.65   $110.60  
  Purchase #5 $116.93   12.629%   $131.6971   $131.70   $131.70   $131.70  
  Purchase #6 $151.48   9.803%   $166.3296   $166.33   $166.35   $166.30  
  Purchase #7 $106.59   11.270%   $118.6027   $118.60   $118.60   $118.60  
  7 purchase totals = $933.98       $1,020.6472   $1,020.65   $1,020.70   $1,020.60