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 $233.75   3.387%   $241.6671   $241.67   $241.65   $241.70  
  Purchase #2 $49.91   7.413%   $53.6098   $53.61   $53.60   $53.60  
  Purchase #3 $238.59   11.496%   $266.0183   $266.02   $266.00   $266.00  
  Purchase #4 $101.65   8.565%   $110.3563   $110.36   $110.35   $110.40  
  Purchase #5 $156.46   5.541%   $165.1294   $165.13   $165.15   $165.10  
  Purchase #6 $10.41   8.634%   $11.3088   $11.31   $11.30   $11.30  
  Purchase #7 $170.51   3.416%   $176.3346   $176.33   $176.35   $176.30  
  7 purchase totals = $961.28       $1,024.4243   $1,024.43   $1,024.40   $1,024.40