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 $212.33   12.118%   $238.0601   $238.06   $238.05   $238.10  
  Purchase #2 $120.40   11.867%   $134.6879   $134.69   $134.70   $134.70  
  Purchase #3 $146.30   4.328%   $152.6319   $152.63   $152.65   $152.60  
  Purchase #4 $127.87   13.183%   $144.7271   $144.73   $144.75   $144.70  
  Purchase #5 $141.85   4.352%   $148.0233   $148.02   $148.00   $148.00  
  Purchase #6 $143.80   5.288%   $151.4041   $151.40   $151.40   $151.40  
  Purchase #7 $34.97   5.251%   $36.8063   $36.81   $36.80   $36.80  
  7 purchase totals = $927.52       $1,006.3407   $1,006.34   $1,006.35   $1,006.30