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 $96.86   6.527%   $103.1821   $103.18   $103.20   $103.20  
  Purchase #2 $135.32   13.541%   $153.6437   $153.64   $153.65   $153.60  
  Purchase #3 $86.40   5.526%   $91.1745   $91.17   $91.15   $91.20  
  Purchase #4 $192.96   3.581%   $199.8699   $199.87   $199.85   $199.90  
  Purchase #5 $120.90   11.158%   $134.39   $134.39   $134.40   $134.40  
  Purchase #6 $142.53   5.217%   $149.9658   $149.97   $149.95   $150.00  
  Purchase #7 $205.76   3.400%   $212.7558   $212.76   $212.75   $212.80  
  7 purchase totals = $980.73       $1,044.9818   $1,044.98   $1,044.95   $1,045.10