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 $51.36   9.644%   $56.3132   $56.31   $56.30   $56.30  
  Purchase #2 $164.99   4.457%   $172.3436   $172.34   $172.35   $172.30  
  Purchase #3 $66.73   10.850%   $73.9702   $73.97   $73.95   $74.00  
  Purchase #4 $71.57   8.242%   $77.4688   $77.47   $77.45   $77.50  
  Purchase #5 $95.25   12.133%   $106.8067   $106.81   $106.80   $106.80  
  Purchase #6 $79.63   11.108%   $88.4753   $88.48   $88.50   $88.50  
  Purchase #7 $165.52   4.110%   $172.3229   $172.32   $172.30   $172.30  
  7 purchase totals = $695.05       $747.7007   $747.70   $747.65   $747.70