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 $246.42   12.148%   $276.3551   $276.36   $276.35   $276.40  
  Purchase #2 $191.97   6.383%   $204.2234   $204.22   $204.20   $204.20  
  Purchase #3 $178.79   4.722%   $187.2325   $187.23   $187.25   $187.20  
  Purchase #4 $20.76   9.238%   $22.6778   $22.68   $22.70   $22.70  
  Purchase #5 $243.58   8.710%   $264.7958   $264.80   $264.80   $264.80  
  Purchase #6 $53.27   6.190%   $56.5674   $56.57   $56.55   $56.60  
  Purchase #7 $232.39   10.740%   $257.3487   $257.35   $257.35   $257.30  
  7 purchase totals = $1,167.18       $1,269.2007   $1,269.21   $1,269.20   $1,269.20