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 $186.46   13.110%   $210.9049   $210.90   $210.90   $210.90  
  Purchase #2 $65.87   13.343%   $74.659   $74.66   $74.65   $74.70  
  Purchase #3 $167.34   5.657%   $176.8064   $176.81   $176.80   $176.80  
  Purchase #4 $147.99   11.795%   $165.4454   $165.45   $165.45   $165.40  
  Purchase #5 $150.81   13.717%   $171.4966   $171.50   $171.50   $171.50  
  Purchase #6 $41.38   13.555%   $46.9891   $46.99   $47.00   $47.00  
  Purchase #7 $212.84   6.494%   $226.6618   $226.66   $226.65   $226.70  
  7 purchase totals = $972.69       $1,072.9632   $1,072.97   $1,072.95   $1,073.00