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 $71.34   7.705%   $76.8367   $76.84   $76.85   $76.80  
  Purchase #2 $227.74   6.858%   $243.3584   $243.36   $243.35   $243.40  
  Purchase #3 $24.57   4.347%   $25.6381   $25.64   $25.65   $25.60  
  Purchase #4 $192.99   5.802%   $204.1873   $204.19   $204.20   $204.20  
  Purchase #5 $79.26   7.553%   $85.2465   $85.25   $85.25   $85.20  
  Purchase #6 $150.73   6.135%   $159.9773   $159.98   $160.00   $160.00  
  Purchase #7 $182.38   12.864%   $205.8414   $205.84   $205.85   $205.80  
  7 purchase totals = $929.01       $1,001.0857   $1,001.10   $1,001.15   $1,001.00