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 $22.93   5.481%   $24.1868   $24.19   $24.20   $24.20  
  Purchase #2 $94.57   8.552%   $102.6576   $102.66   $102.65   $102.70  
  Purchase #3 $114.58   8.739%   $124.5931   $124.59   $124.60   $124.60  
  Purchase #4 $103.92   4.415%   $108.5081   $108.51   $108.50   $108.50  
  Purchase #5 $202.74   8.865%   $220.7129   $220.71   $220.70   $220.70  
  Purchase #6 $56.37   8.822%   $61.343   $61.34   $61.35   $61.30  
  Purchase #7 $23.94   5.464%   $25.2481   $25.25   $25.25   $25.20  
  7 purchase totals = $619.05       $667.2496   $667.25   $667.25   $667.20