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 $145.29   9.637%   $159.2916   $159.29   $159.30   $159.30  
  Purchase #2 $241.79   8.871%   $263.2392   $263.24   $263.25   $263.20  
  Purchase #3 $49.95   9.361%   $54.6258   $54.63   $54.65   $54.60  
  Purchase #4 $115.88   9.194%   $126.534   $126.53   $126.55   $126.50  
  Purchase #5 $52.96   9.668%   $58.0802   $58.08   $58.10   $58.10  
  Purchase #6 $129.37   12.442%   $145.4662   $145.47   $145.45   $145.50  
  Purchase #7 $194.56   11.360%   $216.662   $216.66   $216.65   $216.70  
  7 purchase totals = $929.80       $1,023.8990   $1,023.90   $1,023.95   $1,023.90