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 $237.49   7.706%   $255.791   $255.79   $255.80   $255.80  
  Purchase #2 $60.56   4.614%   $63.3542   $63.35   $63.35   $63.40  
  Purchase #3 $191.30   10.710%   $211.7882   $211.79   $211.80   $211.80  
  Purchase #4 $213.99   11.717%   $239.0632   $239.06   $239.05   $239.10  
  Purchase #5 $165.41   5.262%   $174.1139   $174.11   $174.10   $174.10  
  Purchase #6 $135.39   9.343%   $148.0395   $148.04   $148.05   $148.00  
  Purchase #7 $209.36   3.413%   $216.5055   $216.51   $216.50   $216.50  
  7 purchase totals = $1,213.50       $1,308.6555   $1,308.65   $1,308.65   $1,308.70