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 $60.89   12.574%   $68.5463   $68.55   $68.55   $68.50  
  Purchase #2 $23.64   4.363%   $24.6714   $24.67   $24.65   $24.70  
  Purchase #3 $204.48   8.387%   $221.6297   $221.63   $221.65   $221.60  
  Purchase #4 $238.39   8.356%   $258.3099   $258.31   $258.30   $258.30  
  Purchase #5 $82.29   12.469%   $92.5507   $92.55   $92.55   $92.60  
  Purchase #6 $219.60   12.197%   $246.3846   $246.38   $246.40   $246.40  
  Purchase #7 $94.60   6.337%   $100.5948   $100.59   $100.60   $100.60  
  7 purchase totals = $923.89       $1,012.6874   $1,012.68   $1,012.70   $1,012.70