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 $233.27   13.765%   $265.3796   $265.38   $265.40   $265.40  
  Purchase #2 $206.36   10.844%   $228.7377   $228.74   $228.75   $228.70  
  Purchase #3 $241.74   10.273%   $266.574   $266.57   $266.55   $266.60  
  Purchase #4 $169.84   6.620%   $181.0834   $181.08   $181.10   $181.10  
  Purchase #5 $68.85   4.717%   $72.0977   $72.10   $72.10   $72.10  
  Purchase #6 $18.92   4.816%   $19.8312   $19.83   $19.85   $19.80  
  Purchase #7 $15.44   8.772%   $16.7944   $16.79   $16.80   $16.80  
  7 purchase totals = $954.42       $1,050.4980   $1,050.49   $1,050.55   $1,050.50