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 $173.65   12.457%   $195.2816   $195.28   $195.30   $195.30  
  Purchase #2 $121.55   8.303%   $131.6423   $131.64   $131.65   $131.60  
  Purchase #3 $178.59   9.706%   $195.9239   $195.92   $195.90   $195.90  
  Purchase #4 $204.37   9.370%   $223.5195   $223.52   $223.50   $223.50  
  Purchase #5 $195.90   7.854%   $211.286   $211.29   $211.30   $211.30  
  Purchase #6 $39.33   5.260%   $41.3988   $41.40   $41.40   $41.40  
  Purchase #7 $180.40   11.548%   $201.2326   $201.23   $201.25   $201.20  
  7 purchase totals = $1,093.79       $1,200.2847   $1,200.28   $1,200.30   $1,200.20