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 $163.57   12.572%   $184.134   $184.13   $184.15   $184.10  
  Purchase #2 $243.27   8.647%   $264.3056   $264.31   $264.30   $264.30  
  Purchase #3 $16.94   13.631%   $19.2491   $19.25   $19.25   $19.20  
  Purchase #4 $33.40   7.294%   $35.8362   $35.84   $35.85   $35.80  
  Purchase #5 $152.43   9.755%   $167.2995   $167.30   $167.30   $167.30  
  Purchase #6 $86.72   8.165%   $93.8007   $93.80   $93.80   $93.80  
  Purchase #7 $248.89   4.692%   $260.5679   $260.57   $260.55   $260.60  
  7 purchase totals = $945.22       $1,025.1930   $1,025.20   $1,025.20   $1,025.10