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 $94.33   7.111%   $101.0378   $101.04   $101.05   $101.00  
  Purchase #2 $10.73   7.824%   $11.5695   $11.57   $11.55   $11.60  
  Purchase #3 $36.27   6.824%   $38.7451   $38.75   $38.75   $38.70  
  Purchase #4 $241.78   5.757%   $255.6993   $255.70   $255.70   $255.70  
  Purchase #5 $57.52   6.119%   $61.0396   $61.04   $61.05   $61.00  
  Purchase #6 $181.61   13.319%   $205.7986   $205.80   $205.80   $205.80  
  Purchase #7 $80.67   9.443%   $88.2877   $88.29   $88.30   $88.30  
  7 purchase totals = $702.91       $762.1776   $762.19   $762.20   $762.10