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 $102.66   13.209%   $116.2204   $116.22   $116.20   $116.20  
  Purchase #2 $200.41   9.586%   $219.6213   $219.62   $219.60   $219.60  
  Purchase #3 $54.54   6.323%   $57.9886   $57.99   $58.00   $58.00  
  Purchase #4 $246.35   9.841%   $270.5933   $270.59   $270.60   $270.60  
  Purchase #5 $217.70   13.647%   $247.4095   $247.41   $247.40   $247.40  
  Purchase #6 $246.57   7.171%   $264.2515   $264.25   $264.25   $264.30  
  Purchase #7 $9.33   12.672%   $10.5123   $10.51   $10.50   $10.50  
  7 purchase totals = $1,077.56       $1,186.5969   $1,186.59   $1,186.55   $1,186.60