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 $180.47   13.154%   $204.209   $204.21   $204.20   $204.20  
  Purchase #2 $175.44   8.395%   $190.1682   $190.17   $190.15   $190.20  
  Purchase #3 $203.87   9.673%   $223.5903   $223.59   $223.60   $223.60  
  Purchase #4 $78.57   9.311%   $85.8857   $85.89   $85.90   $85.90  
  Purchase #5 $247.27   5.467%   $260.7883   $260.79   $260.80   $260.80  
  Purchase #6 $88.65   6.696%   $94.586   $94.59   $94.60   $94.60  
  Purchase #7 $8.91   8.295%   $9.6491   $9.65   $9.65   $9.60  
  7 purchase totals = $983.18       $1,068.8766   $1,068.89   $1,068.90   $1,068.90