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 $203.94   6.311%   $216.8107   $216.81   $216.80   $216.80  
  Purchase #2 $228.93   6.428%   $243.6456   $243.65   $243.65   $243.60  
  Purchase #3 $228.76   12.366%   $257.0485   $257.05   $257.05   $257.00  
  Purchase #4 $106.44   3.764%   $110.4464   $110.45   $110.45   $110.40  
  Purchase #5 $53.57   6.281%   $56.9347   $56.93   $56.95   $56.90  
  Purchase #6 $111.36   6.736%   $118.8612   $118.86   $118.85   $118.90  
  Purchase #7 $234.95   4.294%   $245.0388   $245.04   $245.05   $245.00  
  7 purchase totals = $1,167.95       $1,248.7859   $1,248.79   $1,248.80   $1,248.60