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 $69.62   6.744%   $74.3152   $74.32   $74.30   $74.30  
  Purchase #2 $231.55   3.672%   $240.0525   $240.05   $240.05   $240.10  
  Purchase #3 $59.33   10.654%   $65.651   $65.65   $65.65   $65.70  
  Purchase #4 $156.91   5.579%   $165.664   $165.66   $165.65   $165.70  
  Purchase #5 $82.36   8.809%   $89.6151   $89.62   $89.60   $89.60  
  Purchase #6 $95.34   7.311%   $102.3103   $102.31   $102.30   $102.30  
  Purchase #7 $84.91   12.590%   $95.6002   $95.60   $95.60   $95.60  
  7 purchase totals = $780.02       $833.2083   $833.21   $833.15   $833.30