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 $216.61   4.619%   $226.6152   $226.62   $226.60   $226.60  
  Purchase #2 $194.53   6.631%   $207.4293   $207.43   $207.45   $207.40  
  Purchase #3 $215.39   13.197%   $243.815   $243.82   $243.80   $243.80  
  Purchase #4 $45.58   7.674%   $49.0778   $49.08   $49.10   $49.10  
  Purchase #5 $31.69   7.219%   $33.9777   $33.98   $34.00   $34.00  
  Purchase #6 $102.40   9.582%   $112.212   $112.21   $112.20   $112.20  
  Purchase #7 $137.52   4.182%   $143.2711   $143.27   $143.25   $143.30  
  7 purchase totals = $943.72       $1,016.3981   $1,016.41   $1,016.40   $1,016.40