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 $232.87   4.852%   $244.1689   $244.17   $244.15   $244.20  
  Purchase #2 $129.52   10.753%   $143.4473   $143.45   $143.45   $143.40  
  Purchase #3 $147.27   5.311%   $155.0915   $155.09   $155.10   $155.10  
  Purchase #4 $57.94   10.282%   $63.8974   $63.90   $63.90   $63.90  
  Purchase #5 $77.55   13.622%   $88.1139   $88.11   $88.10   $88.10  
  Purchase #6 $242.31   13.283%   $274.496   $274.50   $274.50   $274.50  
  Purchase #7 $51.55   10.471%   $56.9478   $56.95   $56.95   $56.90  
  7 purchase totals = $939.01       $1,026.1628   $1,026.17   $1,026.15   $1,026.10