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 $45.68   8.402%   $49.518   $49.52   $49.50   $49.50  
  Purchase #2 $236.48   5.232%   $248.8526   $248.85   $248.85   $248.90  
  Purchase #3 $211.32   10.213%   $232.9021   $232.90   $232.90   $232.90  
  Purchase #4 $133.41   12.370%   $149.9128   $149.91   $149.90   $149.90  
  Purchase #5 $131.58   9.500%   $144.0801   $144.08   $144.10   $144.10  
  Purchase #6 $137.52   13.565%   $156.1746   $156.17   $156.15   $156.20  
  Purchase #7 $101.48   13.840%   $115.5248   $115.52   $115.50   $115.50  
  7 purchase totals = $997.47       $1,096.9650   $1,096.95   $1,096.90   $1,097.00