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 $188.36   8.360%   $204.1069   $204.11   $204.10   $204.10  
  Purchase #2 $173.51   11.782%   $193.9529   $193.95   $193.95   $194.00  
  Purchase #3 $89.53   4.473%   $93.5347   $93.53   $93.55   $93.50  
  Purchase #4 $169.68   5.279%   $178.6374   $178.64   $178.65   $178.60  
  Purchase #5 $221.78   3.277%   $229.0477   $229.05   $229.05   $229.00  
  Purchase #6 $120.49   11.433%   $134.2656   $134.27   $134.25   $134.30  
  Purchase #7 $240.96   11.698%   $269.1475   $269.15   $269.15   $269.10  
  7 purchase totals = $1,204.31       $1,302.6927   $1,302.70   $1,302.70   $1,302.60