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 $236.65   6.562%   $252.179   $252.18   $252.20   $252.20  
  Purchase #2 $65.77   6.465%   $70.022   $70.02   $70.00   $70.00  
  Purchase #3 $132.35   3.621%   $137.1424   $137.14   $137.15   $137.10  
  Purchase #4 $75.57   12.451%   $84.9792   $84.98   $85.00   $85.00  
  Purchase #5 $193.97   9.122%   $211.6639   $211.66   $211.65   $211.70  
  Purchase #6 $57.96   3.182%   $59.8043   $59.80   $59.80   $59.80  
  Purchase #7 $17.63   6.435%   $18.7645   $18.76   $18.75   $18.80  
  7 purchase totals = $779.90       $834.5553   $834.54   $834.55   $834.60