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 $197.91   9.182%   $216.0821   $216.08   $216.10   $216.10  
  Purchase #2 $160.87   6.712%   $171.6676   $171.67   $171.65   $171.70  
  Purchase #3 $106.31   10.206%   $117.16   $117.16   $117.15   $117.20  
  Purchase #4 $214.96   5.398%   $226.5635   $226.56   $226.55   $226.60  
  Purchase #5 $230.87   5.343%   $243.2054   $243.21   $243.20   $243.20  
  Purchase #6 $167.33   3.839%   $173.7538   $173.75   $173.75   $173.80  
  Purchase #7 $194.65   5.707%   $205.7587   $205.76   $205.75   $205.80  
  7 purchase totals = $1,272.90       $1,354.1911   $1,354.19   $1,354.15   $1,354.40