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 $71.74   5.744%   $75.8607   $75.86   $75.85   $75.90  
  Purchase #2 $228.35   5.815%   $241.6286   $241.63   $241.65   $241.60  
  Purchase #3 $151.49   13.270%   $171.5927   $171.59   $171.60   $171.60  
  Purchase #4 $243.38   8.200%   $263.3372   $263.34   $263.35   $263.30  
  Purchase #5 $159.89   9.584%   $175.2139   $175.21   $175.20   $175.20  
  Purchase #6 $19.52   5.452%   $20.5842   $20.58   $20.60   $20.60  
  Purchase #7 $224.87   11.615%   $250.9887   $250.99   $251.00   $251.00  
  7 purchase totals = $1,099.24       $1,199.2060   $1,199.20   $1,199.25   $1,199.20