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 $75.34   11.692%   $84.1488   $84.15   $84.15   $84.10  
  Purchase #2 $199.38   6.628%   $212.5949   $212.59   $212.60   $212.60  
  Purchase #3 $219.57   4.572%   $229.6087   $229.61   $229.60   $229.60  
  Purchase #4 $122.92   9.780%   $134.9416   $134.94   $134.95   $134.90  
  Purchase #5 $222.81   3.862%   $231.4149   $231.41   $231.40   $231.40  
  Purchase #6 $10.62   9.761%   $11.6566   $11.66   $11.65   $11.70  
  Purchase #7 $116.25   4.721%   $121.7382   $121.74   $121.75   $121.70  
  7 purchase totals = $966.89       $1,026.1037   $1,026.10   $1,026.10   $1,026.00