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 $103.44   9.569%   $113.3382   $113.34   $113.35   $113.30  
  Purchase #2 $59.56   12.488%   $66.9979   $67.00   $67.00   $67.00  
  Purchase #3 $81.55   8.739%   $88.6767   $88.68   $88.70   $88.70  
  Purchase #4 $162.47   13.853%   $184.977   $184.98   $185.00   $185.00  
  Purchase #5 $196.28   8.162%   $212.3004   $212.30   $212.30   $212.30  
  Purchase #6 $135.33   3.819%   $140.4983   $140.50   $140.50   $140.50  
  Purchase #7 $244.73   12.364%   $274.9884   $274.99   $275.00   $275.00  
  7 purchase totals = $983.36       $1,081.7769   $1,081.79   $1,081.85   $1,081.80