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 $198.45   3.254%   $204.9076   $204.91   $204.90   $204.90  
  Purchase #2 $118.99   4.478%   $124.3184   $124.32   $124.30   $124.30  
  Purchase #3 $58.50   3.423%   $60.5025   $60.50   $60.50   $60.50  
  Purchase #4 $57.95   8.734%   $63.0114   $63.01   $63.00   $63.00  
  Purchase #5 $211.32   4.330%   $220.4702   $220.47   $220.45   $220.50  
  Purchase #6 $71.50   3.607%   $74.079   $74.08   $74.10   $74.10  
  Purchase #7 $113.37   5.449%   $119.5475   $119.55   $119.55   $119.50  
  7 purchase totals = $830.08       $866.8366   $866.84   $866.80   $866.80