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 $223.75   10.394%   $247.0066   $247.01   $247.00   $247.00  
  Purchase #2 $178.55   13.692%   $202.9971   $203.00   $203.00   $203.00  
  Purchase #3 $154.27   4.731%   $161.5685   $161.57   $161.55   $161.60  
  Purchase #4 $74.80   4.137%   $77.8945   $77.89   $77.90   $77.90  
  Purchase #5 $51.74   7.743%   $55.7462   $55.75   $55.75   $55.70  
  Purchase #6 $161.68   12.370%   $181.6798   $181.68   $181.70   $181.70  
  Purchase #7 $197.85   4.540%   $206.8324   $206.83   $206.85   $206.80  
  7 purchase totals = $1,042.64       $1,133.7251   $1,133.73   $1,133.75   $1,133.70