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 $187.37   11.602%   $209.1087   $209.11   $209.10   $209.10  
  Purchase #2 $152.98   10.491%   $169.0291   $169.03   $169.05   $169.00  
  Purchase #3 $189.98   12.106%   $212.979   $212.98   $213.00   $213.00  
  Purchase #4 $85.69   10.490%   $94.6789   $94.68   $94.70   $94.70  
  Purchase #5 $77.30   13.132%   $87.451   $87.45   $87.45   $87.50  
  Purchase #6 $203.47   6.436%   $216.5653   $216.57   $216.55   $216.60  
  Purchase #7 $153.98   7.706%   $165.8457   $165.85   $165.85   $165.80  
  7 purchase totals = $1,050.77       $1,155.6577   $1,155.67   $1,155.70   $1,155.70