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 $87.57   8.179%   $94.7324   $94.73   $94.75   $94.70  
  Purchase #2 $73.84   3.478%   $76.4082   $76.41   $76.40   $76.40  
  Purchase #3 $131.38   5.133%   $138.1237   $138.12   $138.10   $138.10  
  Purchase #4 $44.33   3.716%   $45.9773   $45.98   $46.00   $46.00  
  Purchase #5 $203.84   4.147%   $212.2932   $212.29   $212.30   $212.30  
  Purchase #6 $22.32   7.232%   $23.9342   $23.93   $23.95   $23.90  
  Purchase #7 $174.80   12.540%   $196.7199   $196.72   $196.70   $196.70  
  7 purchase totals = $738.08       $788.1889   $788.18   $788.20   $788.10