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 $68.89   5.199%   $72.4716   $72.47   $72.45   $72.50  
  Purchase #2 $230.96   3.406%   $238.8265   $238.83   $238.85   $238.80  
  Purchase #3 $107.64   11.154%   $119.6462   $119.65   $119.65   $119.60  
  Purchase #4 $203.48   5.820%   $215.3225   $215.32   $215.30   $215.30  
  Purchase #5 $145.29   6.710%   $155.039   $155.04   $155.05   $155.00  
  Purchase #6 $211.42   6.226%   $224.583   $224.58   $224.60   $224.60  
  Purchase #7 $239.59   3.467%   $247.8966   $247.90   $247.90   $247.90  
  7 purchase totals = $1,207.27       $1,273.7854   $1,273.79   $1,273.80   $1,273.70