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 $194.63   3.381%   $201.2104   $201.21   $201.20   $201.20  
  Purchase #2 $8.57   3.515%   $8.8712   $8.87   $8.85   $8.90  
  Purchase #3 $62.43   3.349%   $64.5208   $64.52   $64.50   $64.50  
  Purchase #4 $240.76   11.206%   $267.7396   $267.74   $267.75   $267.70  
  Purchase #5 $17.25   10.852%   $19.122   $19.12   $19.10   $19.10  
  Purchase #6 $8.30   11.322%   $9.2397   $9.24   $9.25   $9.20  
  Purchase #7 $244.95   4.710%   $256.4871   $256.49   $256.50   $256.50  
  7 purchase totals = $776.89       $827.1908   $827.19   $827.15   $827.10