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 $58.97   3.589%   $61.0864   $61.09   $61.10   $61.10  
  Purchase #2 $213.26   7.234%   $228.6872   $228.69   $228.70   $228.70  
  Purchase #3 $165.35   5.394%   $174.269   $174.27   $174.25   $174.30  
  Purchase #4 $240.32   10.224%   $264.8903   $264.89   $264.90   $264.90  
  Purchase #5 $122.78   5.609%   $129.6667   $129.67   $129.65   $129.70  
  Purchase #6 $158.97   12.338%   $178.5837   $178.58   $178.60   $178.60  
  Purchase #7 $29.96   7.415%   $32.1815   $32.18   $32.20   $32.20  
  7 purchase totals = $989.61       $1,069.3648   $1,069.37   $1,069.40   $1,069.50