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 $80.79   9.288%   $88.2938   $88.29   $88.30   $88.30  
  Purchase #2 $89.37   8.134%   $96.6394   $96.64   $96.65   $96.60  
  Purchase #3 $49.74   3.874%   $51.6669   $51.67   $51.65   $51.70  
  Purchase #4 $202.88   5.304%   $213.6408   $213.64   $213.65   $213.60  
  Purchase #5 $202.68   11.652%   $226.2963   $226.30   $226.30   $226.30  
  Purchase #6 $127.82   6.571%   $136.2191   $136.22   $136.20   $136.20  
  Purchase #7 $203.90   3.551%   $211.1405   $211.14   $211.15   $211.10  
  7 purchase totals = $957.18       $1,023.8968   $1,023.90   $1,023.90   $1,023.80