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 $73.57   5.294%   $77.4648   $77.46   $77.45   $77.50  
  Purchase #2 $229.84   11.145%   $255.4557   $255.46   $255.45   $255.50  
  Purchase #3 $107.90   9.492%   $118.1419   $118.14   $118.15   $118.10  
  Purchase #4 $204.76   5.586%   $216.1979   $216.20   $216.20   $216.20  
  Purchase #5 $187.56   9.161%   $204.7424   $204.74   $204.75   $204.70  
  Purchase #6 $39.33   3.158%   $40.572   $40.57   $40.55   $40.60  
  Purchase #7 $234.71   9.655%   $257.3713   $257.37   $257.35   $257.40  
  7 purchase totals = $1,077.67       $1,169.9460   $1,169.94   $1,169.90   $1,170.00