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 $206.96   9.694%   $227.0227   $227.02   $227.00   $227.00  
  Purchase #2 $87.52   9.297%   $95.6567   $95.66   $95.65   $95.70  
  Purchase #3 $205.61   12.217%   $230.7294   $230.73   $230.75   $230.70  
  Purchase #4 $233.58   13.634%   $265.4263   $265.43   $265.45   $265.40  
  Purchase #5 $166.72   8.486%   $180.8679   $180.87   $180.85   $180.90  
  Purchase #6 $180.99   13.260%   $204.9893   $204.99   $205.00   $205.00  
  Purchase #7 $25.53   9.249%   $27.8913   $27.89   $27.90   $27.90  
  7 purchase totals = $1,106.91       $1,232.5836   $1,232.59   $1,232.60   $1,232.60