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 $203.60   13.243%   $230.5627   $230.56   $230.55   $230.60  
  Purchase #2 $31.33   5.349%   $33.0058   $33.01   $33.00   $33.00  
  Purchase #3 $68.32   5.329%   $71.9608   $71.96   $71.95   $72.00  
  Purchase #4 $249.60   4.345%   $260.4451   $260.45   $260.45   $260.40  
  Purchase #5 $198.52   4.495%   $207.4435   $207.44   $207.45   $207.40  
  Purchase #6 $166.66   9.241%   $182.0611   $182.06   $182.05   $182.10  
  Purchase #7 $109.32   11.687%   $122.0962   $122.10   $122.10   $122.10  
  7 purchase totals = $1,027.35       $1,107.5752   $1,107.58   $1,107.55   $1,107.60