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 $247.59   13.695%   $281.4975   $281.50   $281.50   $281.50  
  Purchase #2 $67.44   12.441%   $75.8302   $75.83   $75.85   $75.80  
  Purchase #3 $201.49   3.280%   $208.0989   $208.10   $208.10   $208.10  
  Purchase #4 $170.84   6.279%   $181.567   $181.57   $181.55   $181.60  
  Purchase #5 $61.79   3.269%   $63.8099   $63.81   $63.80   $63.80  
  Purchase #6 $168.59   12.614%   $189.8559   $189.86   $189.85   $189.90  
  Purchase #7 $167.43   13.862%   $190.6391   $190.64   $190.65   $190.60  
  7 purchase totals = $1,085.17       $1,191.2985   $1,191.31   $1,191.30   $1,191.30