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 $198.98   11.186%   $221.2379   $221.24   $221.25   $221.20  
  Purchase #2 $97.65   4.794%   $102.3313   $102.33   $102.35   $102.30  
  Purchase #3 $50.37   13.154%   $56.9957   $57.00   $57.00   $57.00  
  Purchase #4 $117.68   10.343%   $129.8516   $129.85   $129.85   $129.90  
  Purchase #5 $171.49   5.831%   $181.4896   $181.49   $181.50   $181.50  
  Purchase #6 $72.65   6.738%   $77.5452   $77.55   $77.55   $77.50  
  Purchase #7 $231.40   10.572%   $255.8636   $255.86   $255.85   $255.90  
  7 purchase totals = $940.22       $1,025.3149   $1,025.32   $1,025.35   $1,025.30