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 $197.65   4.183%   $205.9177   $205.92   $205.90   $205.90  
  Purchase #2 $90.31   4.754%   $94.6033   $94.60   $94.60   $94.60  
  Purchase #3 $171.58   13.663%   $195.023   $195.02   $195.00   $195.00  
  Purchase #4 $71.35   5.232%   $75.083   $75.08   $75.10   $75.10  
  Purchase #5 $28.46   12.781%   $32.0975   $32.10   $32.10   $32.10  
  Purchase #6 $196.39   12.489%   $220.9171   $220.92   $220.90   $220.90  
  Purchase #7 $211.89   3.195%   $218.6599   $218.66   $218.65   $218.70  
  7 purchase totals = $967.63       $1,042.3015   $1,042.30   $1,042.25   $1,042.30