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 $91.38   3.593%   $94.6633   $94.66   $94.65   $94.70  
  Purchase #2 $187.90   3.509%   $194.4934   $194.49   $194.50   $194.50  
  Purchase #3 $16.84   6.280%   $17.8976   $17.90   $17.90   $17.90  
  Purchase #4 $183.34   10.311%   $202.2442   $202.24   $202.25   $202.20  
  Purchase #5 $138.35   12.731%   $155.9633   $155.96   $155.95   $156.00  
  Purchase #6 $219.94   12.233%   $246.8453   $246.85   $246.85   $246.80  
  Purchase #7 $117.29   4.857%   $122.9868   $122.99   $123.00   $123.00  
  7 purchase totals = $955.04       $1,035.0939   $1,035.09   $1,035.10   $1,035.10