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 $202.38   11.671%   $225.9998   $226.00   $226.00   $226.00  
  Purchase #2 $76.74   4.514%   $80.204   $80.20   $80.20   $80.20  
  Purchase #3 $242.63   8.237%   $262.6154   $262.62   $262.60   $262.60  
  Purchase #4 $52.96   9.421%   $57.9494   $57.95   $57.95   $57.90  
  Purchase #5 $207.62   11.733%   $231.9801   $231.98   $232.00   $232.00  
  Purchase #6 $191.76   8.452%   $207.9676   $207.97   $207.95   $208.00  
  Purchase #7 $20.52   4.108%   $21.363   $21.36   $21.35   $21.40  
  7 purchase totals = $994.61       $1,088.0793   $1,088.08   $1,088.05   $1,088.10