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 $179.83   6.525%   $191.5639   $191.56   $191.55   $191.60  
  Purchase #2 $93.62   9.279%   $102.307   $102.31   $102.30   $102.30  
  Purchase #3 $120.86   4.223%   $125.9639   $125.96   $125.95   $126.00  
  Purchase #4 $159.36   3.690%   $165.2404   $165.24   $165.25   $165.20  
  Purchase #5 $216.52   11.165%   $240.6945   $240.69   $240.70   $240.70  
  Purchase #6 $44.49   6.694%   $47.4682   $47.47   $47.45   $47.50  
  Purchase #7 $79.37   11.201%   $88.2602   $88.26   $88.25   $88.30  
  7 purchase totals = $894.05       $961.4981   $961.49   $961.45   $961.60