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 $16.93   10.481%   $18.7044   $18.70   $18.70   $18.70  
  Purchase #2 $246.53   11.376%   $274.5753   $274.58   $274.60   $274.60  
  Purchase #3 $31.59   9.641%   $34.6356   $34.64   $34.65   $34.60  
  Purchase #4 $202.93   4.777%   $212.624   $212.62   $212.60   $212.60  
  Purchase #5 $192.50   13.786%   $219.0381   $219.04   $219.05   $219.00  
  Purchase #6 $134.34   11.371%   $149.6158   $149.62   $149.60   $149.60  
  Purchase #7 $49.41   5.525%   $52.1399   $52.14   $52.15   $52.10  
  7 purchase totals = $874.23       $961.3331   $961.34   $961.35   $961.20