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 $176.71   13.509%   $200.5818   $200.58   $200.60   $200.60  
  Purchase #2 $41.50   10.743%   $45.9583   $45.96   $45.95   $46.00  
  Purchase #3 $25.47   9.685%   $27.9368   $27.94   $27.95   $27.90  
  Purchase #4 $171.33   12.767%   $193.2037   $193.20   $193.20   $193.20  
  Purchase #5 $47.54   3.260%   $49.0898   $49.09   $49.10   $49.10  
  Purchase #6 $232.35   9.530%   $254.493   $254.49   $254.50   $254.50  
  Purchase #7 $226.85   7.148%   $243.0652   $243.07   $243.05   $243.10  
  7 purchase totals = $921.75       $1,014.3286   $1,014.33   $1,014.35   $1,014.40