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 $51.68   7.568%   $55.5911   $55.59   $55.60   $55.60  
  Purchase #2 $181.99   8.760%   $197.9323   $197.93   $197.95   $197.90  
  Purchase #3 $128.30   10.693%   $142.0191   $142.02   $142.00   $142.00  
  Purchase #4 $170.71   12.349%   $191.791   $191.79   $191.80   $191.80  
  Purchase #5 $56.32   8.352%   $61.0238   $61.02   $61.00   $61.00  
  Purchase #6 $240.64   6.380%   $255.9928   $255.99   $256.00   $256.00  
  Purchase #7 $11.98   8.653%   $13.0166   $13.02   $13.00   $13.00  
  7 purchase totals = $841.62       $917.3667   $917.36   $917.35   $917.30