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 $89.67   5.483%   $94.5866   $94.59   $94.60   $94.60  
  Purchase #2 $204.54   11.634%   $228.3362   $228.34   $228.35   $228.30  
  Purchase #3 $193.83   6.416%   $206.2661   $206.27   $206.25   $206.30  
  Purchase #4 $232.97   6.636%   $248.4299   $248.43   $248.45   $248.40  
  Purchase #5 $131.95   13.734%   $150.072   $150.07   $150.05   $150.10  
  Purchase #6 $87.44   11.737%   $97.7028   $97.70   $97.70   $97.70  
  Purchase #7 $202.43   4.402%   $211.341   $211.34   $211.35   $211.30  
  7 purchase totals = $1,142.83       $1,236.7346   $1,236.74   $1,236.75   $1,236.70