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 $86.51   7.778%   $93.2387   $93.24   $93.25   $93.20  
  Purchase #2 $90.63   6.694%   $96.6968   $96.70   $96.70   $96.70  
  Purchase #3 $203.53   9.562%   $222.9915   $222.99   $223.00   $223.00  
  Purchase #4 $245.97   9.279%   $268.7936   $268.79   $268.80   $268.80  
  Purchase #5 $198.63   13.363%   $225.1729   $225.17   $225.15   $225.20  
  Purchase #6 $50.94   11.231%   $56.6611   $56.66   $56.65   $56.70  
  Purchase #7 $62.94   6.604%   $67.0966   $67.10   $67.10   $67.10  
  7 purchase totals = $939.15       $1,030.6512   $1,030.65   $1,030.65   $1,030.70