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 $43.78   12.271%   $49.1522   $49.15   $49.15   $49.20  
  Purchase #2 $219.62   5.636%   $231.9978   $232.00   $232.00   $232.00  
  Purchase #3 $199.30   8.612%   $216.4637   $216.46   $216.45   $216.50  
  Purchase #4 $62.37   11.859%   $69.7665   $69.77   $69.75   $69.80  
  Purchase #5 $23.75   8.551%   $25.7809   $25.78   $25.80   $25.80  
  Purchase #6 $222.86   6.574%   $237.5108   $237.51   $237.50   $237.50  
  Purchase #7 $172.94   13.641%   $196.5307   $196.53   $196.55   $196.50  
  7 purchase totals = $944.62       $1,027.2026   $1,027.20   $1,027.20   $1,027.30