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 $106.36   12.295%   $119.437   $119.44   $119.45   $119.40  
  Purchase #2 $204.79   9.221%   $223.6737   $223.67   $223.65   $223.70  
  Purchase #3 $193.93   8.155%   $209.745   $209.75   $209.75   $209.70  
  Purchase #4 $7.65   10.144%   $8.426   $8.43   $8.45   $8.40  
  Purchase #5 $111.29   5.160%   $117.0326   $117.03   $117.05   $117.00  
  Purchase #6 $203.77   9.645%   $223.4236   $223.42   $223.40   $223.40  
  Purchase #7 $157.42   6.518%   $167.6806   $167.68   $167.70   $167.70  
  7 purchase totals = $985.21       $1,069.4185   $1,069.42   $1,069.45   $1,069.30