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 $19.73   11.507%   $22.0003   $22.00   $22.00   $22.00  
  Purchase #2 $179.37   6.817%   $191.5977   $191.60   $191.60   $191.60  
  Purchase #3 $231.65   6.521%   $246.7559   $246.76   $246.75   $246.80  
  Purchase #4 $230.54   11.700%   $257.5132   $257.51   $257.50   $257.50  
  Purchase #5 $116.81   9.390%   $127.7785   $127.78   $127.80   $127.80  
  Purchase #6 $169.56   11.501%   $189.0611   $189.06   $189.05   $189.10  
  Purchase #7 $58.30   3.774%   $60.5002   $60.50   $60.50   $60.50  
  7 purchase totals = $1,005.96       $1,095.2069   $1,095.21   $1,095.20   $1,095.30