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 $248.58   4.197%   $259.0129   $259.01   $259.00   $259.00  
  Purchase #2 $202.82   12.172%   $227.5073   $227.51   $227.50   $227.50  
  Purchase #3 $247.53   3.133%   $255.2851   $255.29   $255.30   $255.30  
  Purchase #4 $204.52   12.743%   $230.582   $230.58   $230.60   $230.60  
  Purchase #5 $181.86   3.513%   $188.2487   $188.25   $188.25   $188.20  
  Purchase #6 $23.89   5.351%   $25.1684   $25.17   $25.15   $25.20  
  Purchase #7 $23.33   5.320%   $24.5712   $24.57   $24.55   $24.60  
  7 purchase totals = $1,132.53       $1,210.3756   $1,210.38   $1,210.35   $1,210.40