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 $61.47   10.363%   $67.8401   $67.84   $67.85   $67.80  
  Purchase #2 $179.94   9.762%   $197.5057   $197.51   $197.50   $197.50  
  Purchase #3 $164.43   5.113%   $172.8373   $172.84   $172.85   $172.80  
  Purchase #4 $99.66   5.798%   $105.4383   $105.44   $105.45   $105.40  
  Purchase #5 $98.94   7.244%   $106.1072   $106.11   $106.10   $106.10  
  Purchase #6 $180.77   10.103%   $199.0332   $199.03   $199.05   $199.00  
  Purchase #7 $210.95   8.273%   $228.4019   $228.40   $228.40   $228.40  
  7 purchase totals = $996.16       $1,077.1637   $1,077.17   $1,077.20   $1,077.00