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 $61.60   13.421%   $69.8673   $69.87   $69.85   $69.90  
  Purchase #2 $187.91   8.540%   $203.9575   $203.96   $203.95   $204.00  
  Purchase #3 $118.27   5.365%   $124.6152   $124.62   $124.60   $124.60  
  Purchase #4 $32.65   11.685%   $36.4652   $36.47   $36.45   $36.50  
  Purchase #5 $134.54   11.298%   $149.7403   $149.74   $149.75   $149.70  
  Purchase #6 $73.27   12.625%   $82.5203   $82.52   $82.50   $82.50  
  Purchase #7 $216.67   11.144%   $240.8157   $240.82   $240.80   $240.80  
  7 purchase totals = $824.91       $907.9815   $908.00   $907.90   $908.00