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 $191.25   7.680%   $205.938   $205.94   $205.95   $205.90  
  Purchase #2 $91.55   7.684%   $98.5847   $98.58   $98.60   $98.60  
  Purchase #3 $172.35   8.349%   $186.7395   $186.74   $186.75   $186.70  
  Purchase #4 $229.25   12.463%   $257.8214   $257.82   $257.80   $257.80  
  Purchase #5 $94.52   6.297%   $100.4719   $100.47   $100.45   $100.50  
  Purchase #6 $32.39   7.258%   $34.7409   $34.74   $34.75   $34.70  
  Purchase #7 $172.54   3.750%   $179.0103   $179.01   $179.00   $179.00  
  7 purchase totals = $983.85       $1,063.3067   $1,063.30   $1,063.30   $1,063.20