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 $173.76   13.560%   $197.3219   $197.32   $197.30   $197.30  
  Purchase #2 $246.78   11.454%   $275.0462   $275.05   $275.05   $275.00  
  Purchase #3 $66.67   12.587%   $75.0618   $75.06   $75.05   $75.10  
  Purchase #4 $174.78   5.767%   $184.8596   $184.86   $184.85   $184.90  
  Purchase #5 $244.41   13.250%   $276.7943   $276.79   $276.80   $276.80  
  Purchase #6 $109.82   9.210%   $119.9344   $119.93   $119.95   $119.90  
  Purchase #7 $224.81   6.868%   $240.25   $240.25   $240.25   $240.30  
  7 purchase totals = $1,241.03       $1,369.2682   $1,369.26   $1,369.25   $1,369.30