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 $232.38   6.510%   $247.5079   $247.51   $247.50   $247.50  
  Purchase #2 $196.56   3.175%   $202.8008   $202.80   $202.80   $202.80  
  Purchase #3 $81.60   8.828%   $88.8036   $88.80   $88.80   $88.80  
  Purchase #4 $207.91   3.288%   $214.7461   $214.75   $214.75   $214.70  
  Purchase #5 $109.59   11.701%   $122.4131   $122.41   $122.40   $122.40  
  Purchase #6 $220.94   11.539%   $246.4343   $246.43   $246.45   $246.40  
  Purchase #7 $45.89   3.716%   $47.5953   $47.60   $47.60   $47.60  
  7 purchase totals = $1,094.87       $1,170.3011   $1,170.30   $1,170.30   $1,170.20