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 $202.90   13.761%   $230.8211   $230.82   $230.80   $230.80  
  Purchase #2 $132.73   12.107%   $148.7996   $148.80   $148.80   $148.80  
  Purchase #3 $121.66   9.834%   $133.624   $133.62   $133.60   $133.60  
  Purchase #4 $15.84   5.389%   $16.6936   $16.69   $16.70   $16.70  
  Purchase #5 $194.62   4.296%   $202.9809   $202.98   $203.00   $203.00  
  Purchase #6 $66.42   13.219%   $75.2001   $75.20   $75.20   $75.20  
  Purchase #7 $233.79   9.261%   $255.4413   $255.44   $255.45   $255.40  
  7 purchase totals = $967.96       $1,063.5606   $1,063.55   $1,063.55   $1,063.50