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 $243.33   8.352%   $263.6529   $263.65   $263.65   $263.70  
  Purchase #2 $212.59   3.648%   $220.3453   $220.35   $220.35   $220.30  
  Purchase #3 $18.79   4.689%   $19.6711   $19.67   $19.65   $19.70  
  Purchase #4 $187.79   4.625%   $196.4753   $196.48   $196.50   $196.50  
  Purchase #5 $38.36   8.693%   $41.6946   $41.69   $41.70   $41.70  
  Purchase #6 $88.57   11.165%   $98.4588   $98.46   $98.45   $98.50  
  Purchase #7 $194.41   9.565%   $213.0053   $213.01   $213.00   $213.00  
  7 purchase totals = $983.84       $1,053.3033   $1,053.31   $1,053.30   $1,053.40