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 $142.28   6.861%   $152.0418   $152.04   $152.05   $152.00  
  Purchase #2 $104.86   13.143%   $118.6417   $118.64   $118.65   $118.60  
  Purchase #3 $247.99   11.757%   $277.1462   $277.15   $277.15   $277.10  
  Purchase #4 $91.55   5.611%   $96.6869   $96.69   $96.70   $96.70  
  Purchase #5 $180.40   12.582%   $203.0979   $203.10   $203.10   $203.10  
  Purchase #6 $9.47   3.507%   $9.8021   $9.80   $9.80   $9.80  
  Purchase #7 $71.41   5.184%   $75.1119   $75.11   $75.10   $75.10  
  7 purchase totals = $847.96       $932.5285   $932.53   $932.55   $932.40