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 $174.42   11.134%   $193.8399   $193.84   $193.85   $193.80  
  Purchase #2 $241.47   12.512%   $271.6827   $271.68   $271.70   $271.70  
  Purchase #3 $156.76   10.481%   $173.19   $173.19   $173.20   $173.20  
  Purchase #4 $135.85   9.759%   $149.1076   $149.11   $149.10   $149.10  
  Purchase #5 $72.92   9.144%   $79.5878   $79.59   $79.60   $79.60  
  Purchase #6 $92.52   3.295%   $95.5685   $95.57   $95.55   $95.60  
  Purchase #7 $29.99   9.756%   $32.9158   $32.92   $32.90   $32.90  
  7 purchase totals = $903.93       $995.8923   $995.90   $995.90   $995.90