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 $195.34   13.570%   $221.8476   $221.85   $221.85   $221.80  
  Purchase #2 $131.31   12.183%   $147.3075   $147.31   $147.30   $147.30  
  Purchase #3 $244.51   12.587%   $275.2865   $275.29   $275.30   $275.30  
  Purchase #4 $239.37   6.226%   $254.2732   $254.27   $254.25   $254.30  
  Purchase #5 $7.30   3.731%   $7.5724   $7.57   $7.55   $7.60  
  Purchase #6 $34.56   6.634%   $36.8527   $36.85   $36.85   $36.90  
  Purchase #7 $104.73   8.529%   $113.6624   $113.66   $113.65   $113.70  
  7 purchase totals = $957.12       $1,056.8023   $1,056.80   $1,056.75   $1,056.90