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 $56.38   4.287%   $58.797   $58.80   $58.80   $58.80  
  Purchase #2 $113.52   11.268%   $126.3114   $126.31   $126.30   $126.30  
  Purchase #3 $111.93   7.235%   $120.0281   $120.03   $120.05   $120.00  
  Purchase #4 $161.42   5.148%   $169.7299   $169.73   $169.75   $169.70  
  Purchase #5 $240.34   11.683%   $268.4189   $268.42   $268.40   $268.40  
  Purchase #6 $49.72   12.569%   $55.9693   $55.97   $55.95   $56.00  
  Purchase #7 $207.32   4.356%   $216.3509   $216.35   $216.35   $216.40  
  7 purchase totals = $940.63       $1,015.6055   $1,015.61   $1,015.60   $1,015.60