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 $65.62   4.566%   $68.6162   $68.62   $68.60   $68.60  
  Purchase #2 $33.68   7.251%   $36.1221   $36.12   $36.10   $36.10  
  Purchase #3 $117.25   12.546%   $131.9602   $131.96   $131.95   $132.00  
  Purchase #4 $63.83   9.764%   $70.0624   $70.06   $70.05   $70.10  
  Purchase #5 $187.46   6.310%   $199.2887   $199.29   $199.30   $199.30  
  Purchase #6 $225.97   10.218%   $249.0596   $249.06   $249.05   $249.10  
  Purchase #7 $188.83   12.319%   $212.092   $212.09   $212.10   $212.10  
  7 purchase totals = $882.64       $967.2012   $967.20   $967.15   $967.30