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 $83.86   8.604%   $91.0753   $91.08   $91.10   $91.10  
  Purchase #2 $241.87   9.328%   $264.4316   $264.43   $264.45   $264.40  
  Purchase #3 $69.81   11.461%   $77.8109   $77.81   $77.80   $77.80  
  Purchase #4 $62.84   5.472%   $66.2786   $66.28   $66.30   $66.30  
  Purchase #5 $132.96   12.845%   $150.0387   $150.04   $150.05   $150.00  
  Purchase #6 $85.71   10.819%   $94.983   $94.98   $95.00   $95.00  
  Purchase #7 $205.72   7.514%   $221.1778   $221.18   $221.20   $221.20  
  7 purchase totals = $882.77       $965.7959   $965.80   $965.90   $965.80